core: Introduce a context serial number.
* src/context.h: Include stdint.h. (struct gpgme_context): Add field 'serial'. (CTXSERIAL): New. * src/gpgme.c: (last_ctx_serial): New. (gpgme_new): Set serial. * src/gpgme.c: Change trace calls to use the serial. * src/wait.c (_gpgme_add_io_cb): Ditto (_gpgme_remove_io_cb): Ditto.
- Signed-off-by: Werner Koch <wk@gnupg.org>