This header is set to 1 by dbrw.rewrite to indicate that an error
occurred during the rewrite.
* New flags: regex and eq
One of this flags can appear in the fourth column of the returned data
set. The 'eq' flag instructs dbrw.rewrite to use exact string match,
instead of regular expressions. The 'regex' flag instructs it to use
regular expression matching. It is the default.
* Improve error handling in mysql submodule
Previously, error codes ER_PARSE_ERROR and ER_EMPTY_QUERY were treated
as permanent conditions, causing mysql connection to be closed and
disabled. This is no longer the case, as they both can well mean a
transient condition (e.g. ER_PARSE_ERROR returned for the 'Illegal mix
of collations' error).