* data/yacc.c: Say "parser skeleton" rather than "file", since

* data/yacc.c: Say "parser skeleton" rather than "file", since
it's no longer just a file.
* data/glr.c: Grant a special exception for C GLR parsers, that
reads like the already-existing exception for C LALR(1) parsers.
* data/glr.cc: Likewise.
* data/lalr1.cc: Likewise.
* data/location.cc: Likewise.
* data/yacc.c: Reword the "written by" statement to clarify that
it was the parser skeleton, not the entire output file.
* data/glr.c: Written by Paul Hilfinger.
* data/glr.cc: Written by Akim Demaille.
* data/lalr1.cc: Likewise.