Update pdbfile.py

Added ability to download pdb or compressed pdb from url.
Update pdbfile.py

changed urllib2 to urllib
Update test_pdb.py

added test to see if pdb url works correctly
Merge branch 'patch-1' of github.com:cxhernandez/mdtraj into pdb-url
Changed the detection of URLS to use urlparse from the stdlib instead of just checking for http://
Changed the detection of URLS to use urlparse from the stdlib instead of just checking for http://
remove print
change back imports
py3 stringio fix
try to fix failure
I HATE UNICODE BULLSHIT
Merge pull request #335 from rmcgibbo/pdb-url

load_pdb from URL