gpgscm: Add 'finally', rework all macros.
* tests/gpgscm/init.scm (finally): New macro. * tests/gpgscm/tests.scm (letfd): Rewrite. (with-working-directory): Likewise. (with-temporary-working-directory): Likewise. (lettmp): Likewise.
Rewrite all our macros using 'define-macro'. Use the new control flow
mechanism 'finally', or 'dynamic-wind' where appropriate. Make sure
the macros are hygienic. Reduce code duplication.
- Signed-off-by: Justus Winter <email@example.com>