Wave front bug-fix and comment-fix

This is about #528 (Bug in wave front processing),

To enable WPP (--WaveFrontSynchro=1), in EncSlice.cpp

bool isLastCTUinWPP = wavefrontsEnabled && ((ctuRsAddr + 1 % widthInCtus) == tileXPosInCtus);

should be replaced with

bool isLastCTUinWPP = wavefrontsEnabled && (((ctuRsAddr + 1) % widthInCtus) == tileXPosInCtus);

Some wrong software comments on WPP are also fixed.

Note: combination usage of WPP and tile needs more changes.