Add an optional --logfile argument to std::test::test_main and to
compiletest.
Use this features and the new 'check-summary.py' script to
summarise all the tests performed by the 'check' target. This is
a short term fix for #2075.
Now that core exports "option" as a synonym for option::t, search-and-
replace option::t with option.
The only place that still refers to option::t are the modules in libcore
that use option, because fixing this requires a new snapshot
(forthcoming).
