changed background index to complain about uniqueness #1091

Sends an error to the client instead of turning into a foreground index build.
Merge pull request #1093 from Tokutek/unique-hot-index

changed background index to complain about uniqueness

fixes #1091
changed migration to just warn about missing indexes instead of blocking to build them #1045
Merge pull request #1092 from Tokutek/migration-indexes

changed migration to just warn about missing indexes instead of blocking to build them

fixes #1091
Merge branch 'bugfixes/tokumx-1.4'