The MySQL server uses Henry Spencer's library for regular
expressions to support the REGEXP/RLIKE string operator.
This changeset adapts a recent fix from the upstream for
better 32-bit compatiblity. (Note that we cannot simply use
the current upstream version as a drop-in replacement
for the version used by the server as the latter has
been extended to understand MySQL charsets etc.)

(Adds unittest to 5.5 mergeset.)