* src/gpgme.h.in (gpgme_op_revsig_start, gpgme_op_revsig): New.
(GPGME_REVSIG_LFSEP): New.
* src/context.h (ctx_op_data_id_t): Add OPDATA_REVSIG.
* src/revsig.c: New.
* src/Makefile.am (main_sources): Add revsig.
* src/libgpgme.vers, src/gpgme.def: Add gpgme_op_revsig and
gpgme_op_revsig_start.
* src/engine.h, src/engine.c: (_gpgme_engine_op_revsig): New.
* src/engine-backend.h (engine_ops): Add 'revsig' and adjust all
engine initializers.
* src/engine-gpg.c (gpg_revsig): New.
(_gpgme_engine_ops_gpg): Set revsig to gpg_revsig.
* doc/gpgme.texi: Document new functions.
* tests/run-keysign.c: Add option --revoke.