Update pegasus-halt to fix POSIX compliance issue, bug on OSs where SH-> dash

[ahnitz]

Pegasus-halt is not currently POSIX compliant. The main issue is actually the 'function' declaration. Given that the top line tells the script to use 'sh' to run the script, this can be a problem on operating systems which default 'sh' to be a POSIX-compliant shell.

On our cluster for example 'sh' is a link to 'dash' which is pretty strict on this. Here are some minimal changes to get it working.