* src/context.h (gpgme_context): Extend with trust_model.
* src/engine-gpg.c (engine_gpg): Extend with trust_model.
(gpg_set_engine_flags): Take trust_model from context.
(build_argv): Handle trust_model.
(gpg_release): Free trust_model.
* src/gpgme.c (gpgme_set_ctx_flag): Handle trust-model flag.
(gpgme_release): Release trust-model.
* doc/gpgme.texi: Document new flag for gpgme_set_ctx_flag.
(Context Flags): New subsection for the context flags.
* tests/run-keylist.c (show_usage, main): Add new --trust-model
parameter.