Add missing undocs

this adds the missing undocumented opcodes to ca65 6502X target, and a little bit of test code.

i have no idea how the changes in src/sim65/main.c made it into this request, they were not commited to this branch at all, ignore that (or just merge it as well =P)
> mh well, that depends on how portable you want it to be... to signal failure to the parent program, EXIT_FAILURE should be used.

Surely.

> mind you, you can not safely distinguish between the test program returning a value and sim65 failing unless you don't use EXIT_FAILURE in either (because your custom value in one may match EXIT_FAILURE in the other).

Surely.

> to make it really 100% i would include the respective header files of the host system in the build process of the tests and then generate proper return codes that do not conflict. 

I presume we both don't want such a heavyweight process for this rather minor issue.

> alternatively just use hardcoded value in both and live with the possibility of breakage on some obscure operating system.

I'd rather not change the source of the test programs. How about just presuming that the test programs don't use anything beside EXIT_SUCCESS and EXIT_FAILURE. Then we could write here `EXIT_FAILURE + 1`. I know that this isn't perfectly correct but to me it seems appropriate for the usecase at hand.