Fix the raw-compression version of the logic for checking the disk image
we're going to eventually re-instantiate after skipping updates.
Reference #984, #991.
If tests set WIREDTIGER_HOME, they must clear it before finishing, because other tests call `wiredtiger_open` with no home directory and expect it to be ".".

refs #992
Merge branch 'develop' into optional-verbose
Merge branch 'optional-verbose' into optional-verbose-inline