gpgscm: Handle exceptions in the transformation monad.
* tests/gpgscm/tests.scm (pipe:do): Raise errors.
(tr:spawn): Catch and return errors.
(tr:call-with-content): Likewise.
(tr:{open,write-to,pipe-do,assert-identity,assert-weak-identity}):
Adapt.- Signed-off-by: Justus Winter <justus@g10code.com>