Index: openacs-4/packages/acs-tcl/acs-tcl.info
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/acs-tcl.info,v
diff -u -N -r1.95.2.1 -r1.95.2.2
--- openacs-4/packages/acs-tcl/acs-tcl.info	15 Feb 2019 11:03:57 -0000	1.95.2.1
+++ openacs-4/packages/acs-tcl/acs-tcl.info	5 Jun 2019 10:26:31 -0000	1.95.2.2
@@ -9,7 +9,7 @@
     <implements-subsite-p>f</implements-subsite-p>
     <inherit-templates-p>t</inherit-templates-p>
     
-    <version name="5.10.0d24" url="http://openacs.org/repository/download/apm/acs-tcl-5.10.0d24.apm">
+    <version name="5.10.0d25" url="http://openacs.org/repository/download/apm/acs-tcl-5.10.0d25.apm">
         <owner url="http://openacs.org">OpenACS</owner>
         <summary>The Kernel Tcl API library.</summary>
         <release-date>2017-08-06</release-date>
@@ -18,7 +18,7 @@
         <license>GPL version 2</license>
         <maturity>3</maturity>
 
-        <provides url="acs-tcl" version="5.10.0d24"/>
+        <provides url="acs-tcl" version="5.10.0d25"/>
         <requires url="acs-bootstrap-installer" version="5.10.0d4"/>
         <requires url="acs-kernel" version="5.10.0d0"/>
 
Index: openacs-4/packages/acs-tcl/tcl/00-canisue-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/Attic/00-canisue-procs.tcl,v
diff -u -N
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ openacs-4/packages/acs-tcl/tcl/00-canisue-procs.tcl	5 Jun 2019 10:26:31 -0000	1.1.2.1
@@ -0,0 +1,72 @@
+ad_library {
+
+    An API for checking optional features (name inspired by caniuse.com)
+
+    @creation-date 4th June 2019
+    @author Gustaf Neumann
+}
+
+namespace eval ::acs {
+    ad_proc -public icanuse {feature} {
+
+        Check, if a (previously registered) feature can be used in an
+        installation. These features are typically version dependent
+        features of NaviServer. The checking of the availability of
+        these feratures is typically more complex than a plain "info
+        commands ...".
+
+        @param feature name for a feature, can contain blanks
+        @return boolean value
+
+    } {
+        return [info exists ::acs::caniuse($feature)]
+    }
+
+    ad_proc -public register_icanuse {feature condition} {
+
+        Registry function for acs::caniuse.
+
+        @param feature name for a feature, can contain blanks
+        @param condition expression to determine availability
+    } {
+        set success 0
+        try {
+            expr $condition
+        } on ok {result} {
+            set success $result
+        } on error {errorMsg} {
+            # just use the default
+            ns_log warning "registry for caniuse $feature -> $errorMsg"
+        }
+        if {$success} {
+            set ::acs::caniuse($feature) 1
+        }
+        ns_log notice "... I can use $feature -> $success"
+    }
+
+    ad_proc -private cmd_has_subcommand {cmd subcommand} {
+
+        Helper proc abusing error messages to determine, whether as
+        submethod is available.
+
+    } {
+        catch [list $cmd ""] errorMsg
+        return [expr {" $subcommand" in [split $errorMsg ","]}]
+    }
+}
+# Notice: can use 'ns_db currenthandles'
+
+::acs::register_icanuse "ns_db currenthandles" [acs::cmd_has_subcommand ns_db currenthandles]
+::acs::register_icanuse "ns_server ummap" [acs::cmd_has_subcommand ns_server unmap]
+#
+# "ns_server ummap" was introduced in NaviServer at the same time as
+# "ns_conn partialtimes" but the latter would requires a connection
+# (which is not available during loading).
+#
+::acs::register_icanuse "ns_conn partialtimes" [acs::icanuse "ns_server ummap"]
+
+# Local variables:
+#    mode: tcl
+#    tcl-indent-level: 4
+#    indent-tabs-mode: nil
+# End:
Index: openacs-4/packages/acs-tcl/tcl/00-database-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/00-database-procs.tcl,v
diff -u -N -r1.126.2.4 -r1.126.2.5
--- openacs-4/packages/acs-tcl/tcl/00-database-procs.tcl	28 Mar 2019 21:11:22 -0000	1.126.2.4
+++ openacs-4/packages/acs-tcl/tcl/00-database-procs.tcl	5 Jun 2019 10:26:31 -0000	1.126.2.5
@@ -525,20 +525,10 @@
     return $pool
 }
 
+if {[acs::icanuse "ns_db currenthandles"]} {
 
-set useNsdbCurrentHandles 0
-try {
-    ns_db x
-} on error {errorMsg} {
-    if {"currenthandles," in [split $errorMsg " "]} {
-        ns_log notice "can use 'ns_db currenthandles'"
-        set useNsdbCurrentHandles 1
-    } else {
-        ns_log notice "cannot use 'ns_db currenthandles'"
-    }
-}
+    ns_log notice "... I can use 'ns_db currenthandles'"
 
-if {$useNsdbCurrentHandles} {
     #
     # This branch uses "ns_db currenthandles" to implement
     # "db_with_handle" instead of the old approach based on the global
@@ -738,6 +728,7 @@
     # This is the legacy branch without [ns_db currenthandles], using
     # the global state variables.
     #
+    ns_log notice "... cannot use 'ns_db currenthandles'"
 
     ad_proc -public db_with_handle {
         { -dbn "" }