Streamline Capture-IR handling and integrity test.

Change the handling of the "-ircapture" and "-irmask" parameters
to be slightly more sensible, given that the JTAG spec describes
what is required, and that we already require that conformance in
one place.  IR scan returns some bitstring with LSBs "01".

 - First, provide and use default values that satisfy the IEEE spec.
   Existing TAP configs will override the defaults, but those parms
   are no longer required.

 - Second, warn if any TAP gets set up to violate the JTAG spec.
   It's likely a bug, but maybe not; else this should be an error.
   Improve the related diagnostics to say which TAP is affected.

And associated minor fixes/cleanups to comments and diagnostics.


git-svn-id: svn://svn.berlios.de/openocd/trunk@2758 b42882b7-edfa-0310-969c-e2dbd0fdcd60