Fixed and simplified shared photon counter increments in distribPhotons() and distribPhotonContribs(). These now use a temporary variable preIncPhotonCnt to store the counter's value before increment in order to check for overflow. This check is now also triggered when the last photon from the current partition is emitted, to ensure there are no pending increments when photon distribution completes. The previous bug made this painfully obvious as the number of emitted photons reported to the parent process was always a multiple of PMAP_CNTUPDATE (255), which biased the photon flux normalisation! Also disabled fake contribution photon values in encodeContribs() for first "real world" tests. Also revised mRGBE encode/decode sanity check in encodeContribs(). This was disabled but is now triggered due to erroneous differences in the encoded coefficient indices. TODO.