Compiling php52 against mysqlnd fails, fix this by compiling against mysql_config

It appears that php52 doesn't support mysqlnd or vice versa. In order to support mysql I make php52 compile with the following relevant dynamically prepared flags:

--with-mysqli=/usr/local/Cellar/mysql/5.5.29/bin/mysql_config
--with-mysql=/usr/local/Cellar/mysql/5.5.29/bin/mysql_config
--with-pdo-mysql=/usr/local/Cellar/mysql/5.5.29/bin/mysql_config

In order to avoid duplicating code and to allow me to overwrite the default mysql options from AbstractPhp, I needed to shift some code (the code that adds args to "args" based on build options chosen) from "_install" to "install_args". To me this seems like the better place for the code, but can someone please confirm that this will have no unintended consequences.

I choose to delete the default mysql flags in php52 as opposed to adding them into php53 and php54 because I assume going forward mysqlnd is the preferred method of compilation and we don't want creators of future php-* formulas to need to remember to add the mysql flags.