kcov test coverage reports

The test suite is currently being run with the following environment variables:

• GIT_TEST_OPTS='--kcov'

• GIT_SKIP_TESTS='t3404 t3409 t3410 t3411 t3412 t3414 t3415 t3421 t3425 t3903 t5150 t5801 t6030 t7003 t7401 t7508 t7800 t9901 t5520'

Test coverage reports, sorted by date in reverse:

• 20150702173751-2fdae08/
• 20150702151550-198c5c5/
• 20150502145725-c94dfc2/
• 20150501112915-44af3c9/
• 20150430132408-a75942b/