When the environment variable QTC_FATAL_ASSERTS is not empty, make
QTC_ASSERT abort (or equivalent) when the condition is not met. The
purpose is to make certain debugging cases easier without having users
apply a change and recompile.

Change-Id: I8350ed27f78dca94db0c9848bd8af4b91cec2222
Reviewed-by: hjk <hjk121@nokiamail.com>