Make shell scripts executable with the run command

Products whose type contains "sh" or "bat" should be executable by the run command, by invoking /bin/sh (what about other shells, bash, dash, csh, zsh, etc.?) or cmd.exe.

This should also extend to other types of scripts, including but not limited to:

• AppleScript
• PHP
• Python
• Ruby

Implementation details probably need to be fleshed out more. For maximum flexibility, if a product has only one artifact and that artifact has execute bit set, should we just go ahead and run it without regard to file tags?