bootstrap.php: include User Agent in exception log
bootstrap.php: include User Agent in exception log

This will be useful when debugging issues that may be related to
browser version.

I tried to use `get_browser` instead of directly using the `$_SERVER`
superglobal, but doing so requires maintaining a (large) browscap.ini
file, which is not supplied by the PHP installation.

hemberger/smr,smrealms/smr,smrealms/smr,smrealms/smr,hemberger/smr,hemberger/smr,hemberger/smr