GROOVY-6201  groovysh hangs on Edit command when using terminal editor (vim, nano, etc.) on posix terminals

Pull request for http://jira.codehaus.org/browse/GROOVY-6201

Takes advantage of new methods in Java 1.7's ProcessBuilder to have the editor process inherit I/O from the parent shell process.  This fix allows groovysh to launch terminal-based editors (vim, nano, etc.) on posix terminals.