Fix Page Wrapping

[JonnyWalker]

PySNES currently only supports bank boundary wrapping.

Also an analysis what page wrapping is, could be helpful:
An example:
http://www.6502.org/tutorials/65c816opcodes.html#5.1.1

more: http://www.6502.org/tutorials/65c816opcodes.html#5.22
https://wiki.superfamicom.org/instruction-wrapping

Maybe this is only an issue in emulation mode and not relevant to a SNES emulator..