Fixes a case of breakpoint confusion on resume caused by having two
breakpoints one byte apart. This bug can cause the target program to
resume execution a single byte inside an instruction and crash either
with SIGILL or a SIGSEGV, or misbehave (depending on how the truncated
instruction is decoded).
native.(*Thread).StepInstruction should call FindBreakpoint using
adjustPC==false because at that point the PC of the thread should
already have been adjusted (and it has been).
