Better formatting of log file names

[bs2609]

Currently log files are named like this:
Sun Feb 23 12-07-52 GMT 2014.log

This means files are sorted by day of the week, which doesn't seem very useful.
It would probably be better to name log files something like:
2014-02-23_120752.log

This means logs will appear in chronological order, and it should be easier to find a log from a certain date.