Reworked ENDF tests to use id form for nuc_i

Additionally, made endf.test_u235 fail with a useful error message
when the data file is missing.
merge conflict fixed
tiny formatting fix
cleaned up tests
fixing import style
Add environment PATH to hints to find Cython.
Merge remote-tracking branch 'upstream/staging' into staging
Made test_endf.test_u235() download missing data if necessary
added u235 to ignore
Fixed ENDF bug where it would not read the data in, now it reads the data in
Merge remote-tracking branch 'upstream/staging' into staging
Merge branch 'find_cython_19' into staging
Merge branch 'staging' of github.com:crbates/pyne into crbates-staging
Merge branch 'staging' of github.com:crbates/pyne into crbates-staging
added endf to doc /facepalm
up-date