Keep sub-messages aligned. Fix strings for translation.

Keep sub-messages aligned. Fix strings for translation.

	* src/location.h: (location_print): Add return value.
	* src/location.c: (location_print): Return number of printed
	characters.
	* src/complain.h: Two new functions (complain_at_indent,
	warn_at_indent).
	* src/complain.cpp: Implement the alignment mechanism. Add new
	static variable (indent_ptr). Use and update it (error_message,
	complain_at_indent, warn_at_indent).
	* src/scan-code.l: Fix strings for translations. Use new *_indent
	functions (parse_ref, show_sub_messages).
	* tests/named-ref.at: Adjust testcases.
	* NEWS (2.5): Add an announcement about named references.