Closure compiler does not always detect Java

Problem

Closure Compiler can optionally use a local Java instance and the Google Closure Compiler jar rather than relying on the Google compilation service.

The administration page tests for the presence of Java by running shell_exec('java') and checking for a usage string, however some Java implementations return this as an error response (stderr) instead and so this check fails.

Proposed resolution

Adjust the check so that it includes Java implementations which return an stderr response.