Use os.pathsep for TEXINPUTS and BIBINPUTS

TeX utilities on Windows use ';' as separator. See e.g.
http://tex.stackexchange.com/questions/149714/texmaker-windows-7-dont-use-texinputs-environment-variable
Update util.prog_available for work on Windows
Merge pull request #2 from grv87/master

Small update for portability