Log Message:
Add tcllibc 2.0

This package is the optional part of tcllib 2.0 that allows for
running of embedded c-code in Tcl scripts for improved performance.

I think I might actually prefer for tcllib and tcllibc to be contained
in the same pkgsrc package.  But, I'm not sure how portable tcllibc &
critcl are, as well as there might be some circular dependencies
between tcllib and critcl. So for now have separate packages