get_exe_path without proc filesystem patch

[grgro]

added configure check for extern *__progname, which is then used for
get_exe_path to get the executable name for searching the location trough PATH environment value when there is no proc filesystem available. if search results nothing, try current directory just in case.

(0.8)

[rombust]

Many thanks

The EXEPATH example of ClanLib 0.8 does not segmentation fault on my machine any more :)

Applied the patch to ClanLib 0.8 SVN
Also applied the patch to ClanLib 0.9 SVN