Python: Test for expected schema in Pandas conversion

[asfimport]

An additional safety net for future changes and the check that constructing schemas works as expected.

Reporter: Uwe Korn / @xhochy
Assignee: Uwe Korn / @xhochy

_{Note: This issue was originally created as ARROW-479. Please see the migration documentation for further details.}

[asfimport]

Uwe Korn / @xhochy:
PR: #281

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 281
#281