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.

REFERENCES

@@ -25,8 +25,8 @@ LALR(1) Look-Ahead Sets", ACM Transactions on Programming Languages
 and Systems (TOPLAS) 4, 4 (October 1982), 615-649.  Their
 technique is the standard one now.)
 
-	paul rubin
-	free software foundation
+        paul rubin
+        free software foundation
 
 
 [DeRemer-Pennello reference corrected by Paul Eggert <eggert@cs.ucla.edu>,