new error checking

[Doug Evans]

Hi.

I checked in the following patch which adds some error checking.
All current ports pass, but heads up.

Over time we need to add more and more checks.
Ideally we should always run them, but I wonder if we
need an option to turn them off/on.

2009-09-09  Doug Evans  <dje@sebabeach.org>

	* ifield.scm (ifld-beyond-base?): Remove args base-bitsize,
	total-bitsize.  All callers updated.
	* insn.scm (<insn>): Rename member ifld-values to /insn-value.
	New member /insn-base-value.
	(insn-base-value): New function.
	* mach.scm (/sanity-check-insns): New function.
	(arch-analyze-insns!): Call it.