Added exitCode option to allow execute of programs which don't return a
sensible error code
Correct bug where some commands were recorded as failures when no exitCode option specified
add support callback options, and update test cases;
modify "callback" test case
Merge branch 'master' of git://github.com/uc2dabing/grunt-exec into integration-0.4.2

Conflicts:
	tasks/exec.js
Merge branch 'master' of git://github.com/PeteAppleton/grunt-exec into integration-0.4.2

Conflicts:
	tasks/exec.js
Update README for 0.4.2.