TST/BLD: add proper skips for bad bs4 version
Make sure things are being properly skipped because of a bad bs4 version.

Also adds a 4.2.0 known bad version of bs4 to 26 travis build so that we can verify that tests are being skipped when the version is bad.

O_o travis DL speeds are double digits...so slow...
 @jreback this ok?

just adding bs4 and html5lib to travis python26 build so that we can verify 4.2.0 tests are in fact being skipped. also adds skip messages for things not found
 yes...this looks ok
 i see 0.12 on the horizon :sunrise: 
