qt, tests: Add check for supported versions
* lang/qt/tests/t-encrypt.cpp (decryptSupported): Moved to t-support as loopbackSupported. * lang/qt/tests/t-remarks.cpp: Check for loopbackSupported. * lang/qt/tests/t-support.cpp, lang/qt/tests/t-support.h (loopbackSupported): New.
This ensures that the tests do not fail with GnuPG 2.0.x