tog: add support for commit keywords Allow keywords as arguments to options and operands for the blame, diff, log, and tree commands. Also, return 1 when exiting tog with error rather than 0 so regress can discern success from failure. ok stsp@

tog regress: TAB instruction + test for diff J keymap Add the TAB instruction to the test harness, and a test case for the previous commit: scroll down the log from the diff view with the J keymap when on the last loaded commit. ok stsp@

tog: rename regress test script envvar As per stsp's idea: use a more descriptive name, and use the TOG_TEST_SCRIPT envvar both in tog.c and the test scripts. ok stsp@

tog: basic diff view test and fix hardcoded script path ok stsp@