Minor fixes to frange.

Minor fixes to frange.

Following are a series of cleanups to the frange code in preparation
for a much more invasive patch rewriting the NAN and sign tracking
bits.  Please be patient, as I'm trying to break everything up into
small chunks instead of dropping a mondo patch removing the NAN and
sign tristate handling.

No functional changes.

Regstrapped on x86-64 Linux, plus I ran selftests for
-ffinite-math-only.

gcc/ChangeLog:

	* value-query.cc (range_query::get_tree_range): Remove check for overflow.
	* value-range-pretty-print.cc (vrange_printer::visit): Move read
	of type until after undefined_p is checked.
	* value-range.cc (frange::set): Remove asserts for REAL_CST.
	(frange::contains_p): Tidy up.
	(range_tests_nan):  Add comment.
	* value-range.h (frange::type): Check for undefined_p.
	(frange::set_undefined): Remove set of endpoints.