MMC3 - IRQ timing test fails

[DaveTCode]

This was likely related to #67 but that's now fixed.

[DaveTCode]

Test 2 is the first test in that suite so this could be anything:

set_test 2,"Scanline 0 IRQ should occur later when $2000=$08"
test $08, 0, scanline_0_08 - 1
cmp #$22
jne test_failed

All this is really testing is that when PPUCTRL = 08 (that is, BG is at page 0000 and sprites are page 1000) that the IRQ occurs on a particular cycle. So presumably I'm off by one on the exact cycle I change the VRAM addr on.

Need to compare cycle timings of the IRQ set in me vs mesen