Fix for issue #3442 to support range types in .xql files
PostgreSQL supports range types since 9.5. When using range types,
square braces have to be used in SQL statements. Since OpenACS uses
always Tcl substitution in .xql files, and OpenACS does NOT allow
backslash substitution in these files, square brackets could not be
escaped and therefore not be used in .xql files so far. This change
allows now a developer to deactivate the substitution by passing
e.g. "-subst none" to the db_* command using the .xql file. Valid
values for "-subst" are "all", "none", "vars", and "commands", default
is "all" which is exactly the behavior of before. Therefore, this
change is fully backward compatible.
