The current "checkindex" on startup is very very expensive. This is
like running one of the old school hard drive diagnostic checkers and
usually not a good idea.
But we can do a CRC32 verification of files. We don't even need to
open an indexreader to do this, its much more lightweight.
This option (as well as the existing true/false) are randomized in
tests to find problems.
Also fix bug where use of the current option would always leak
an indexwriter lock.
Closes#9183
027730006b