* src/context.h (struct gpgme_context): New field import_options.
* src/engine-backend.h (struct engine_ops): Add arg import_options to
field 'import'.
* src/engine-gpg.c (gpg_import): Add arg import_options and pass option
--import-options with argument value to gpg.
* src/engine-gpgsm.c (gpgsm_import): Add dummy arg import_options.
* src/engine.c (_gpgme_engine_op_import): Add arg import_options and
pass option to import function of engine.
* src/engine.h (_gpgme_engine_op_import): Add arg import_options.
* src/gpgme.c (gpgme_release): Free 'import_options'.
(gpgme_set_ctx_flag, gpgme_get_ctx_flag): New flag "import-options".
* src/import.c (_gpgme_op_import_start, _gpgme_op_import_keys_start,
_gpgme_op_receive_keys_start): Pass import options stored in context to
_gpgme_engine_op_import.
* tests/run-import.c (show_usage, main): Add option --import-options.