* src/gpgme.h.in (gpgme_op_keysign_start, gpgme_op_keysign): New.
(GPGME_KEYSIGN_LOCAL): New.
(GPGME_KEYSIGN_LFSEP): New.
(GPGME_KEYSIGN_NOEXPIRE): New.
* src/context.h (ctx_op_data_id_t): Add OPDATA_KEYSIGN.
* src/keysign.c: New.
* src/Makefile.am (main_sources): Add keysig.
* src/libgpgme.vers, src/gpgme.def: Add gpgme_op_keysign_start.
* src/engine.c (_gpgme_engine_op_keysign): New.
* src/engine-backend.h (engine_ops): Add 'keysign' and adjust all
engine initializers.
* src/engine-gpg.c (_add_arg): Add args PREFIX and ARGLEN and change
callers to set them.
(add_arg_pfx): New.
(add_arg_len): New.
(gpg_keysign): New.
(_gpgme_engine_ops_gpg): Set keysign to gpg_keysign.
* tests/run-keysign.c: New.
* tests/Makefile.am (noinst_PROGRAMS): Add run-keysign.