Force output_compression Off for downloads

Looks like a long standing, yet-to-be-fixed PHP bug, where
zlib.output_compression can result in the output buffer not completely being
flushed. This is especially critical for downloads where the tail of the
file might be lost.

https://bugs.php.net/bug.php?id=19436
Merge pull request #596 from greezybacon/issue/php-zlib-truncates-download

Turn off output_compression for downloads

Reviewed-By: Peter Rotich <peter@osticket.com>