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.

NEWS

@@ -894,26 +894,26 @@ Bison News
   if the symbols have destructors.  For instance:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
-	| exp "+" exp
-	;
+        | exp "+" exp
+        ;
 
   will trigger a warning about $$ and $5 in the first rule, and $3 in
   the second ($1 is copied to $$ by the default rule).  This example
   most likely contains three errors, and could be rewritten as:
 
      exp: exp "?" exp ":" exp
-	    { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
-	| exp "+" exp
-	    { $$ = $1 ? $1 : $3; if ($1) free ($3); }
-	;
+            { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
+        | exp "+" exp
+            { $$ = $1 ? $1 : $3; if ($1) free ($3); }
+        ;
 
   However, if the original actions were really intended, memory leaks
   and all, the warnings can be suppressed by letting Bison believe the
   values are used, e.g.:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
-	| exp "+" exp         { $$ = $1; (void) $3; }
-	;
+        | exp "+" exp         { $$ = $1; (void) $3; }
+        ;
 
   If there are mid-rule actions, the warning is issued if no action
   uses it.  The following triggers no warning: $1 and $3 are used.
@@ -1157,16 +1157,16 @@ Bison News
   In agreement with POSIX and with other Yaccs, leaving a default
   action is valid when $$ is untyped, and $1 typed:
 
-	untyped: ... typed;
+        untyped: ... typed;
 
   but the converse remains an error:
 
-	typed: ... untyped;
+        typed: ... untyped;
 
 ** Values of mid-rule actions
   The following code:
 
-	foo: { ... } { $$ = $1; } ...
+        foo: { ... } { $$ = $1; } ...
 
   was incorrectly rejected: $1 is defined in the second mid-rule
   action, and is equal to the $$ of the first mid-rule action.