* src/scan-gram.l, src/reader.h (scanner_last_string_free):

* src/scan-gram.l, src/reader.h (scanner_last_string_free):
Restore.
* src/scan-gram.l (last_string): Is global to the file, not to
yylex.
* src/parse-gram.y (input): Don't append the epilogue here,
(epilogue.opt): do it here, and free the scanner's obstack.
* src/reader.c (epilogue_set): Rename as...
(epilogue_augment): this.
* data/c.m4 (b4_epilogue): Defaults to empty.