innodb.doublewrite: Similar to what was done to innodb.101_compatibility,
add an explicit $_ parameter to the Perl unpack function.
Also, fix some diagnostic messages in the Perl code.
innodb.innodb-wl5522-debug: Adjust for the changed error codes and
messages on fault injection.
Syntax. Server support. Test cases.
InnoDB bugfixes:
* don't mess around with system sprintf's, always use my_error() for errors.
* don't use InnoDB internal error codes where OS error codes are expected.
* don't say "file not found", when it was.
