Testsuite: added support for basic result checking.

TODO

src/lib-sieve/sieve-result.c

src/lib-sieve/sieve-result.h

src/testsuite/Makefile.am

src/testsuite/ext-testsuite.c

src/testsuite/testsuite-common.c

src/testsuite/testsuite-common.h

src/testsuite/testsuite-result.c

src/testsuite/testsuite-result.h

src/testsuite/tst-test-error.c

src/testsuite/tst-test-result.c

tests/execute/actions.svtest

tests/execute/actions/fileinto.sieve

tests/execute/actions/redirect.sieve

tests/extensions/reject/execute.svtest

tests/extensions/vacation/execute.svtest

tests/extensions/vacation/execute/action.sieve