When reading the depend.internal file, check only once for every depender
whether it exists, instead of repeatedly in a loop for each dependee. Within
that function it can only change of the depender is removed. This is taken
care of.
This reduces the number of access() calls in kdelibs/khtml from 180000 to
90000 (i.e. 50%), and reduces the time for that (without the actual
scanning) from 0.3 s to 0.21 s on my system.

Alex