The -gnatyr switch is supposed to generate a style warning if the case
of a usage name does not match that of the defining_identifier it
denotes. The warning was missing for component names appearing in record
representation clauses; this patch fixes that bug.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_ch13.adb (Analyze_Record_Representation_Clause): Call
	Set_Entity_With_Checks instead of Set_Entity, so we perform the
	check for correct casing.
	* style.adb (Check_Identifier): Minor comment improvement.
	Cleanup overly complicated code.