Handle PHP config file errors

This patch makes the maxlifetime script tolerant to PHP errors resulting from removed or incorrect config file entries.

These can happen when a normally unused config file gets parsed, in our case this was when we upgraded to PHP 5.4. We fixed the upgrade errors in fpm, but not apache2. The sessionclean script silently failed. This led to a server crash when we ran out of inodes.

The new behavior is for maxlifetime to ignore php.ini files that cause errors rather than to fail noisily; the assumption if there are errors in a config file, it will not be in use.