#79 threads broken in 3.5.1

[Jeff Rogers]

The threading (as used by Direct_Url) doesn't work in
3.5.1. Any attempt to use it gets errors, starting
with "unknown command Stderr" and "package md5 not
found".

I can patch lib/thread.tcl to replace the "Stderr" with
"puts stderr" and add "package require md5" into
Thread_Start, but there may be other initialization
done in the non-thread initialization (like searching
for tcllib) that isn't done properly.