GROOVY-4877: Groovy Console should set the context class loader to the class loader that loaded the script.

All credit belongs to Luke Daley. I just created a pull request out of his patch.
GROOVY-4877: Groovy Console should set the context class loader to the class loader that loaded the script.

Incorporated Graeme and Pauls feedback. The classloader is now only modified for the scope of execution of the script and only if the "useScriptClassLoaderForScriptExecution" is true. "useScriptClassLoaderForScriptExecution" defaults to false and is set to true in the main method.
GROOVY-4877: Groovy Console should set the context class loader to the class loader that loaded the script.

Better name for the local variable which holds the saved ContextClassLoader (as suggested by Paul).
Merge pull request #129 from PascalSchumacher/GROOVY-4877

GROOVY-4877: Groovy Console should set the context class loader to the c...