gmod_src: Added filesystem_steam to project

Revision 809
Added filesystem_steam to projectChanged Files:
[ul]
[li]trunk/src_garrysmod/Garrysmod.sln[/li][li]trunk/src_garrysmod/Posix_Build.sh[/li][li]trunk/src_garrysmod/Target_Folder.bat[/li][li]trunk/src_garrysmod/VPC_Build.bat[/li][/ul]
Committed By Garry Newman

What does it do?

:smug: