Avoid using left-most column STAT3 samples if the left-most column has an
equality constrain and there are inequality constraints on the second column.
An improved method for avoiding the use of the STAT3 samples to compute
the estimated number of outputs when the left-most index is equality
constrained.  This check-in undoes the previous fix and applies a new one.
Add test case for the problem fixed by [127a5b776d].
Make sure signed integer overflow does not cause a segfault while attempting
to read a corrupt database where the header size varint on a record is larger
than the maximum 32-bit signed integer.
Fix a potential buffer overread in sqlite3VdbeRecordCompare() when a
serial_type specifies a field that starts in bounds but is much too large
for the allocated buffer.  Mostly harmless.  The overread is unlikely to
go more than one or two bytes past the end of the buffer.
Fix an incorrect expected result in a test case in corruptG.test.
Fix the CREATE INDEX statement so that trying to create a TEMP index on
a non-TEMP table throws an error rather than segfaulting.