Add support for controlling warnings/errors.

	Add support for controlling warnings/errors.
	Add tests for iformat description errors.
	* dev.scm (cload): New option #:diag.
	* read.scm (<reader>): New member verify-iformat?.
	(/parse-diagnostic, parse-warning): New functions.
	(parse-error): Guts moved to /parse-diagnostic.
	(/set-diagnostic-options!): New function.
	(cpu-load): New arg diagnostic-options, all callers updated.
	Recognize -w diagnostic-option-list.
	* ifield.scm (ifields-base-ifields): Move here from iformat.scm.
	(ifld-simple-ifields, ifields-simple-ifields): New function.
	* insn.scm (/parse-insn-format-iflds): New function.
	(/parse-insn-format): Guts moved to /parse-insn-format-iflds.
	New arg isa, all callers updated.  Do some basic validation of the
	ifield list if requested.
	* mach.scm (/sanity-check-insns): Improve error message text.
	* doc/running.text: Document -w option.

	* ifield.scm (/multi-ifield-parse): Initialize bitrange.