Clean up yacc.c a little.

Clean up yacc.c a little.

* data/yacc.c: Clean up M4 for readability, and make output
whitespace more consistent.  For the main parse function
comment, instead of saying "yyparse or yypush_parse", say either
"yyparse" or "yypush_parse" depending on which it actually is.
(cherry picked from commit bb31eb56abd67c0ccf92244d160855ff06a336ac)

Conflicts:

	src/parse-gram.c
	src/parse-gram.h