php53: import Slackware64 13.37 sources

Import sources from Slackware64 13.37's php package, using that as a base.
13.37 was the last Slackware version to ship PHP 5.3.

NOTE: dropped the PHP source itself as not to clutter the repos (not
      shipping binaries here anyway), fetch it from an external resource
      when needed.  Also unpacked all compressed files, easier to work with
      that way.