Break flag handling

Seth, I noticed a problem in how the break flag is handled.  Based on the MOS 6502 programming manual, I changed a couple of things.

1.  The php command should not modify the break flag.
2.  The brk command should push the break flag on the stack but not change it (page 144 of the manual).  I was surprised by that behavior.  Here is where I got the manual:

http://www.classiccmp.org/cini/pdf/Commodore/KIM-1%20Programming%20Manual.pdf