Push down to libgtop all platform-dependent code
Submitted by Stefano Facchini
There are some "#ifdef linux" in the codebase. If we want to revive libgtop we could think of pushing there all these ifdefs and keep the gui code system-independent.
- RENICE max and min values in procdialogs.h
- writable memory definition in proctable.cpp
- cpu freq. definition in procproperties.cpp
- the kthread conditional in proctable.cpp