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

* 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.