Debugger: make "PPC to x86" open JIT window

The button just silently did nothing if the window wasn't open, with no hint
as to how to make it work.
Merge pull request #800 from FioraAeterna/showdebugjit

Debugger: make "PPC to x86" open JIT window
JIT: correctly set skipNext even if conditional-continue is off

Part 2: I missed the other branch-merging case in the first commit.
Merge pull request #801 from FioraAeterna/mergebranchfix

JIT: correctly set skipNext even if conditional-continue is off
JIT: Don't needlessly flush register state in merged integer+branch code

The actual branch code doesn't flush the register state, so it doesn't make
much sense for the merged optimization to do so either.
Merge pull request #798 from FioraAeterna/integerflush

JIT: Don't needlessly flush register state in merged integer+branch code
Debugger: fix blowup calculation