New versions tlshell and GUI installer

[Siep Kroonenberg]

Installer:
- warning about non-empty target directory
- display of installer revision number
- interaction portable <=> More... fixed

tlshell:
- search path setting under windows
- display of tlmgr- and tlshell revision numbers
- `Restart tlmgr' temporarily commented out until I get it working

Under windows, GUI language can be set only from within tlshell, not
from the command-line. I hope to fix this later.

-- 
Siep Kroonenberg