tests/test-symlinks.out

let run-tests run optional code coverage tests.

to enable, set env var TEST_COVERAGE to non-empty string. run-tests will
print report after running.

after coverage run, file tests/.coverage will contain coverage data. use
tests/coverage.py to get more info, like annotated source code.

adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
! a.c
! dir/a.o
! dir/b.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c