Replace horrible hack with searching for substrings in $argv0 to decide
if tkdemos.tcl was being sourced from a plserver or wish environment.
Tested by Alan W. Irwin <firstname.lastname@example.org> on Linux using
the test_tk_standard_examples and test_wish_standard_examples targets.
Note, the second target had a segfault right after example 33 completed
so investigation of that issue is ongoing.
Since the horrible hack is gone, there is a reasonable chance now that
these two targets (and also the test_interactive target which depends
on them) will also work fine in the installed examples tree. But that
case has not been tested yet.