Do not hardcode quoting style in error messages.

Replace spots in error message specs. where single quotes are hardcoded as `' with
the error_util library's quote/1 constructor.

Fix minor issues with some error messages and add a couple of XXX comments
about some others.

compiler/accumulator.m:
compiler/add_clause.m:
compiler/add_pragma.m:
compiler/add_pred.m:
compiler/add_type.m:
compiler/det_analysis.m:
compiler/det_report.m:
compiler/goal_expr_to_goal.m:
compiler/make_hlds_error.m:
compiler/mercury_compile.m:
compiler/mode_errors.m:
compiler/modes.m:
compiler/modules.m:
compiler/options_file.m:
compiler/post_typecheck.m:
compiler/prog_io.m:
compiler/prog_io_pragma.m:
compiler/simplify_goal.m:
compiler/simplify_proc.m:
compiler/term_constr_errors.m:
compiler/term_errors.m:
compiler/termination.m:
compiler/typecheck.m:
compiler/typecheck_errors.m:
	As above.

tests/invalid/errors.err_exp:
tests/invalid/missing_det_decl.err_exp:
tests/invalid/no_exports.err_exp:
tests/invalid/predmode.err_exp:
tests/invalid/undef_type.err_exp:
	Conform to the above changes.