[Bf-python] Library.Open() - relative paths

[Campbell Barton]

Hi,
Malefico needs to get python to open up relative blend's
say Library.Open('//foo.blend')

Currently this isnt supported because Library.c's  M_Library_Open func 
calls  readblenentry.c's  BLO_blendhandle_from_file that calls
readfile.c's blo_openblenderfile

and
blo_openblenderfile dosnt support relative paths.

Im a bit buisy right now to fix this so Id appreciate it if one of the 
other  c/python'ers  could solve this one.
- Cam