d: Merge upstream dmd 740f3d1ea.

d: Merge upstream dmd 740f3d1ea.

Backports the conversion of the parameter fields debugids and versionids
to Identifiers.  The idea is that Identifiers should be used instead of
C strings where ever possible.

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 740f3d1ea.
	* d-lang.cc (d_handle_option): Use new fields to save debug and
	version levels passed over command-line.
	(d_post_options): Add them to front-end here.