* tests/gpgscm/ffi.scm: Move the customized exception handling and
atexit logic...
* tests/gpgscm/init.scm: ... here.
(throw): Record the current history.
(throw'): New function that is history-aware.
(rethrow): New function.
(*error-hook*): Use the new throw'.
* tests/gpgscm/main.c (load): Fix error handling.
(main): Save and use the 'sc->retcode' as exit code.
* tests/gpgscm/repl.scm (repl): Print call history.
* tests/gpgscm/scheme.c (_Error_1): Make a snapshot of the history,
use it to provide a accurate location of the expression causing the
error at runtime, and hand the history trace to the '*error-hook*'.
(opexe_5): Tag all lists at parse time with the current location.
* tests/gpgscm/tests.scm: Update calls to 'throw', use 'rethrow'.