[Tilesathome] Client logging

[Matthias Julius]

Hi all,

I have prepared another little patch for the client that changes the
date format in the log file to human the readable ISO format that at
least I find easier to understand than the current timestamp.

Also, the patch moves the decision whether to log or not into the
keepLog() function where it is in a central place.

If this makes sense someone could commit that into svn.  And this time
I have double-checked that the client actually still runs...

Matthias