changes for install from repository:
- change labeling of list filter:
* show current channel version (instead of just "current")
* call selector for head packages not "head" but supplemental
- offer on "head" channel just these packages, which are not available
in the current channel (this avoids a potential damage in the
current installation, when somebody tries e.g. to install
a core package from head, which is broken and/or older than
packages in the current channel). Since there is no way to downgrade
packages in OpenACS, such errors might be hard to fix.
- use message keys instead of hard-coded strings for maturity in
www/install/install.tcl
