use a more consistent quoting style.

See <http://lists.gnu.org/archive/html/bug-bison/2012-01/msg00120.html>.
Use quotearg as often as possible instead of leaving the choice of
the quotes to the translators.  Use shorter messages.  Factor similar
messages to a single format, to make localization easier.

	* src/files.c, src/getargs.c, src/muscle-tab.c, src/reader.c
	* src/scan-code.l, src/scan-gram.l, src/symtab.c:
	Use quote() or quotearg_colon() on printf arguments instead of
	quotes in the format string.
	* data/bison.m4: Keep sync with the changes in muscle-tab.c.

	* tests/skeletons.at, tests/input.at, tests/regression.at: Adjust
	expected messages.

src/muscle-tab.h

@@ -20,6 +20,8 @@
 #ifndef MUSCLE_TAB_H_
 # define MUSCLE_TAB_H_
 
+# include <quotearg.h>
+
 # include "location.h"
 
 void muscle_init (void);