Add STDOUT, STDIN, and STDERR to the php-constants list

When we run a PHP program from the command-line (i.e. via the CLI
SAPI) then we have access to the three constants above.  This patch
adds them to the ‘php-constants’ list so that PHP mode will give them
proper highlighting.

Github-issue: 82
Re-define C-M-h to mark-defun instead of c-mark-function

As the code commentary explains, there are situations where
c-mark-function oversteps its bounds and creates a region around more
than just the function at point.  Using mark-defun instead gives us
more ‘natural’ behavior.

This patch adds TatriX Imbra to the list of contributors because he
was the one who not only brought this bug to my attention but provided
the solution of using mark-defun.