global: remove unnecessary horizontal tabs.

This change was made by applying emacs' untabify function to
nearly all files in Bison's repository.  Required tabs in make
files, ChangeLog, regexps, and test code were manually skipped.
Other notable exceptions and changes are listed below.
* bootstrap: Skip because we sync this with gnulib.
* data/m4sugar/foreach.m4
* data/m4sugar/m4sugar.m4: Skip because we sync these with
Autoconf.
* djgpp: Skip because I don't know how to test djgpp properly, and
this code appears to be unmaintained anyway.
* README-hacking (Hacking): Specify that tabs should be avoided
where not required.

src/symtab.h

@@ -39,8 +39,8 @@
 typedef enum
 {
   unknown_sym,          /**< Undefined.  */
-  token_sym,		/**< Terminal. */
-  nterm_sym		/**< Non-terminal. */
+  token_sym,            /**< Terminal. */
+  nterm_sym             /**< Non-terminal. */
 } symbol_class;
 
 
@@ -166,7 +166,7 @@ void symbol_precedence_set (symbol *sym, int prec, assoc a, location loc);
 
 /** Set the \c class associated with \c sym.  */
 void symbol_class_set (symbol *sym, symbol_class class, location loc,
-		       bool declaring);
+                       bool declaring);
 
 /** Set the \c user_token_number associated with \c sym.  */
 void symbol_user_token_number_set (symbol *sym, int user_number, location loc);