Bug #71667: have pdo_dblib emulate how mssql extension names "computed" columns, plug memory leak (PHP-5.6)

[adambaratz]

Full notes are in the bug report I created:
https://bugs.php.net/bug.php?id=71667

The efree() calls could be removed from dblib_stmt.c because free_statement(), which is part of the pdo extension, will do this cleanup before the functions in dblib_stmt.c get called.

I realize that README.GIT-RULES says PRs should be done against PHP-5.6, but that branch is missing changes that my changes are built on top of. I'm happy to update this PR if anyone has guidance there. I'm going to look at master separately and submit another bug/PR if needed.

[weltling]

@adambaratz, thanks for the PR. Looks like i've accidentially broke mergeability base by pushing a parallel patch. I've checked with your patch and adjusted the leak fixing part.

The part with the changing the column names should be discussed. In general, such behavior change should not happen in the middle of a stable series. Please open another PR for this issue, if you think it is critical. I'm going to close this one for now.

Btw ext/pdo_dblb is currently missing active maintanance. It would be great to see someone to step in for at least the regular maintanance.

Thanks!

[php-pulls]

Comment on behalf of ab at php.net:

The leak fixing part is applied to 5.6+. Thanks for your work!

[MiRacLe-RPZ]

@weltling, "computed" column was added in 5.6.16 (with my PR #1386), i think applying this patch safe for stable releases...

[adambaratz]

Thanks for that note @MiRacLe-RPZ. I created a #1780 for discussion of making this change to 5.6. FYI, #1777 is still around for making this change to master.