CPCEC, ZXSEC and CSFEC

What's New:

- minor patch fixing a bug in command-line parameters combined with autorun files: the former could override the later even when the files came last (reported by Cpcitor). Further tweaks in the sound logic and sources to enable compiling the emulators with mono sound, and to improve the audio synchro. Optional surround stereo is available in CPCEC, CSFEC (when there's more than one SID chip) and ZXSEC. X-masking and Y-masking changed again, trying to grow closer to light-and-dark pixel analog screen patterns. X-blending adjusts itself to the machine's video mode, f.e. it will perform simpler pixel blur calculations in CPCEC when MODE 2 isn't selected.