Option to use syslog instead of log file

[rjhughes]

Hi. I'm continuing my quest to make standard services available in roundcube.

Here, I added an option to allow syslog logging, rather than simply writing to a file. Syslog can do anything, it's great. I left the 'file' driver as the default, though.

[thomasb]

I would rather put it the other way round:

if ($CONFIG['log_driver'] == 'syslog') { ... }
else { /* current code */ }

In this case the config option 'log_driver' remains optional.

[rjhughes]

Okay, the latest attachment does it that way -- if you omit the log_driver config statement entirely, it will behave as if you'd said 'file'.

[rjhughes]

Patch against 1186 to allow the use of syslog, but continue to use file-based logging if you don't specify.

[alec]

Added in r1683.