Added start_test() and finish_test() functions to test/common.sh.in.

Added start_test() and finish_test() functions to test/common.sh.in.
See usage information in the (new) cleanup() function in that file.
This allow us to isolate test failures based on naming of individual
tests within a single test file.  As part of this, added set -e to
setup_test().  This required minor updates to test/new/basic and
test/pick/test-stderr to conform.  So, migrated test/new/test-basic
to start_test()/finish_test().