MAINT: Add assertion for incompatible history freq specification. Supplying 1m frequency to history but only providing daily source data resulted in an odd non-descript exception. This adds a specific check and raises a more informative exception.
BLD: Remove numpy 1.8.1 requirement from travis.
MAINT: Test frequency.unit_str instead of frequency string.
TST: Fix history unittest.
BLD: Trying to fix travis.
MAINT: Add custom exception for incompatible history frequency specification.
BLD: Update numpy to 1.8.2
REV: Revert numpy update (back to 1.8.1)

This reverts commit 0eb12156c8e007963029c0faa3d1154902cd873f.
DOC: Add more information to IncompatibleHistoryFrequency message.
Merge branch 'master' of https://github.com/Quantopian/zipline