Update error tests
test/testta5.data

Add some more clip tests
test/testta6.data

First pass at implementing the tile clip. Reasonably accurate wrt basic
understanding of how its supposed to work, not so accurate wrt actual
hardware behaviour
src/pvr2/tacore.c

Fix broken tests
Add more NaN tests
test/testta5.data

Verify that bit 23 doesn't preserve other bits
test/testta.data

Fix parse_float_colour for values <= 0 and qNaN
src/pvr2/tacore.c

Handle NAN vertexes "correctly" (TA treats them as +/- INF)
src/pvr2/tacore.c

Add tile clip parsing
src/pvr2/tacore.c

Add masks on all PVR2 registers
Add missing registers and rename display registers for consistency
src/pvr2/pvr2.c
src/pvr2/pvr2mmio.h

Update the register list to scan the entire 5F8000-5F8200 range (ie all
PVR registers) for writeability
test/testregs.c