Blender Git Loki

fix for crash's in file selector.
- on unix BLI_diskfree was only using 100 chars for the dir name, and
not checking if the name given was longer, increased to FILE_MAXDIR
(160) and added a check, return -1 if its too long.

The file selector only allowed 80 chars to be typed into the directory
entry.

Made the file selector check that the path is less then FILE_MIXDIR, if
you try and enter a path thats longer it will tell you that the path is
too long, before it was writing into other memory and crashing.