instead of letting *every* qmake-based project have recursive check target,
let interested projects "subscribe" to it by adding CONFIG+=testcase_targets
in a central place (.qmake.conf, which Qt itself does via qt_build_config.prf).
Change-Id: Ib13fdd2d3a1adee0c5ad02b6b176a664c583bf9d
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
