Improve more error messages.

Make consistency improvements to error messages concerning initialise, finalise
and mutable declarations.

compiler/make_hlds_error.m:
	Pass a list of format_components to error_if_exported/5 and
	error_is_exported/4 as the item description instead of a string.

compiler/add_pragma.m:
compiler/make_hlds_passes.m:
	Conform to the above change.

compiler/modes.m:
	Use the pragma_decl/1 format component in a couple of spots.

tests/invalid/bad_finalise_decl.err_exp:
tests/invalid/bad_initialise_decl.err_exp:
tests/invalid/bad_mutable.err_exp:
tests/invalid/imported_mode.err_exp:
tests/invalid/not_in_interface.err_exp:
tests/invalid/uniq_mutable.err_exp:
	Conform to the above changes.