fixes #1075 Add a unit test for hot indexing, specifically targetting
the fact that no DBRead/DBWrite lock is held during the build phase,
which is what usually prevents fileops and other bad things from
happening.

fixes #1098 Prevent rename of collections with a background index build
higher in the stack, so we don't do bad things in the cross-database
case.
Merge branch 'bugfixes/tokumx-1.4' into releases/tokumx-1.4