Format and fix CLTools/README.md
Adds button to make CLTools module fail if $? != 0

This option supersedes 'return_code' which does not appear in the wizard
anyway.

It is on by default for new tools.
Merge pull request #958 from VisTrails/cltools-check-exitcode

This looks ok. return_code is for the uncommon case where you want to use non-zero exit code. It is not in the wizard because the interface get easily cluttered when adding too many options.