Handle x-endianess on y-endianess platforms

Closing #2330 , but leaving this here so it'll get picked up one day if needed.
related #2318.

https://groups.google.com/forum/m/#!topic/pydata/ksIPthf2NJI

[jreback]

should raise in constructors on little endian

occasionally causes hard to find issues

should be simple checks

[jorisvandenbossche]

Closing in favor of #4737