Cosa è cambiato in EDuke32, build per build

References: - r3742 - r4038 (fixing savegame screenshots, but introducing the now fixed bug)

This reduces the proportion of time the trig calculations take of the whole preprocessing from 50% to about 13%.

- Use the proper tile sequence when multiple pskies are present in a map. However, there's still only *one* psky chosen at map load time. - Handle three horizfrac cases: * 0, psky always at same level wrt screen * 65536, psky horiz follows camera horiz (e.g. E4L9) * otherwise, fall back to default hard-coded parallax implemented as an angle fraction

Add a test case in test_tileoffsets.map.

This fixes the case marked with the silver letter C in test_tileoffsets.map. The orientation of the sprites is correct (matches classic) as far as I can see, there are now only problems with translation.

Also, add some defines for sprite cstats to build.h (SPR_*) and use them.

The visibility calculation relies on the distance, which might not be entirely accurate in rotatesprite, so maybe it'll be too dark in some cases.