prove(1) can write a summary of its test results and timings into a
cache file, t/.prove, then use this information during later runs for
various purposes. But deleting t/.prove after every test run defeats
this purpose. So do not delete t/.prove as part of "make
DEFAILT_TEST_TARGET=prove test". (Continue to delete the file on
"make clean".)
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>