Mimetype optimization

[Jakub Stachowski]

Hello,

profiling dolphin while opening /usr/bin shows that about 35% of time is spent 
in QRegExp matching called by kmimefactory.cpp: matchFileName. This function 
already contains optimizations: for some simple (but popular) patterns like 
*.something or something* it uses direct comparision instead of QRegExp big 
gun. It looks like:
   if (pattern like *.something && filename long enough to match the pattern)  
compare directly;. 
However for short names (lots of them in /usr/bin) it often falls back to slow 
path. Attached patch changes is to:
if (pattern like *.something) { 
	if (filename not long enough to match) return false;
	else compare directly;
}

and detects patterns without wildcards (is checking for *,? and ] enough?)

Results (measured by callgrind):
Unpatched, for 179 calls to KMimeTypeFactory::findFromFileName
- 5554 calls to QRegExp::exactMatch, which accounts for 35% of CPU time

Patched,  for 150 calls to KMimeTypeFactory::findFromFileName
- QRegExp matched 13 times.  findFromFileName takes 0.67% of CPU time

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