Sort out the situation with kde_file header

[fluxer]

https://github.com/fluxer/kdelibs/blob/master/kdecore/util/kde_file.h is mostly just for convenience right now but does cause some overheat where paths are encoded and decoded (or the other way around) within the use of the definitions in the header. Either the header will go away and a lot of code will have to be adjusted or use of QFile::encodeName() should be reviewed.

Also, QT_SOCKLEN_T and the like can greatly improve the compatibility with various platforms and pretty much every type that is defined in qplatformdefs header should be made use of when possible.