Revert "simplify util:is_unittest function to get rid of a spawn and a ?SCALARIS_RECV"
Revert "simplify util:is_unittest function to get rid of a spawn and a ?SCALARIS_RECV"

This causes problems with older erlang versions, e.g. R14B04, which do not clean up old DOWN messages in demonitor.
caijieming-baidu/scalaris,jvf/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,jvf/scalaris,jvf/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,jvf/scalaris,jvf/scalaris,scalaris-team/scalaris,jvf/scalaris,scalaris-team/scalaris,jvf/scalaris,scalaris-team/scalaris