Have Horde handle PHP legacy error handling.

Have Horde handle PHP legacy error handling.

First - no need to use error_reporting() wrapper anymore - my tests
indicate that as of PHP 5.3, using @foo() is twice as fast.

Next, have all error messages be caught by Horde.  For now, this means
all PHP warnings are output to the Horde DEBUG log rather than to the
screen.  We can play with the various output options in
Horde::errorHandler().

Still need to go through and remove "@" from many function calls.  These
suppressions can result in the WSOD and make for difficult debugging.
Going forward, we should only be concerned with suppressing warnings
that we know aren't critical (e.g. unserialize(), htmlspecialchars()).