Clear up KMesses debug output and make a difference between warnings and errors

[sjors]

Currently, KMess isn't paying a lot of attention to things like failing asserts. In my opinion, we should be able to enable crashing failing asserts, without ever seeing a crash. Also, in my opinion, there are two types of warnings:

- normal warnings, which can be ignored; for example the "Socket can't connect" warnings in P2P, which means we'll just try another one
- important warnings, which shouldn't be ignored, such as the MSN server sending us weird data.

Then, we should do something with these important warnings, for example, save them in a warninglog; when KMess crashed, this warninglog is printed because it may indicate a place where things started going wrong. Or, it should be printed when KMess quits so we know what we should give more attention to.

I think if we lack giving enough attention to warnings, we will more easily introduce bugs into KMess. This bug report also includes "we should fix all failing asserts" (yes, all of them).