Simplify and add invariants to the WhereLoop merging logic inside of
whereLoopInsert().
Fix a harmless uninitialized variable warning.
Additional compiler warning fixes.
Only enable posix_fallocate by default on linux and mac.
Only default HAVE_POSIX_FALLOCATE on for linux, and then only if it is not
previously defined.
Add in the cost of doing a table lookup on OR searches.  Make test case
changes to deal with difference in STAT3 behavior.
Merge in trunk changes to os_unix.c that allow the code to build on
unix platforms that lack posix_fallocate().