* src/files.c, src/files.h (output_infix): New.

(tab_extension): Remove.
(compute_base_names): Compute the former, drop the latter.
* src/output.c (prepare): Insert the muscles `output-infix', and
`output-suffix'.
* src/parse-skel.y (string, string.1): New.
(section.header): Use it.
(section.yacc): Remove.
(prefix): Remove too.
* src/scan-skel.l: Adjust.
* src/bison.simple, src/bison.hairy: Adjust.

src/scan-skel.l

@@ -50,7 +50,6 @@
 "%%{line}"          { return LINE; }
 "%%{skeleton-line}" { return SLINE; }
 
-"%%{yacc}"    { return YACC; }
 "%%{section}" { return SECTION; }
 
 "%%{guards}"   { return GUARDS; }