LocalFlowProcess#getConfigCopy() and LocalFlowProcess#copyConfig(Properties) return an empty Properties

Greetings,

please consider the pull of this changes.

Updated `LocalFlowProcess#getConfigCopy()` and `LocalFlowProcess#copyConfig(Properties)` so they return a copy of the Properties (was returning an empty Properties).
With this modification, the semantic is now equal to HadoopFlowProcess when copying the configuration.

Recently I have started to test Cascading in local and cluster mode and I have been trying to launch flows conveying the configuration files in the .jar (core-site.xml, mapred-site.xml, hbase-site.xml, etc...) and not conveying the configuration files -just the configuration in `new LocalFlowConnector(properties)`-.

* In local mode:

I have found that in some parts of a custo Tap I have to get the configuration (generic parameter=Properties) so I end calling:

    LocalFlowProcess#getConfigCopy()

that returns

    new Properties( config );

if I am not wrong, this las sentence does not return a copy of the config properties, but only one with the set defaults (but in practice, empty). Taken from JDK source:

    /**
     * Creates an empty property list with the specified defaults.
     *
     * @param defaults the defaults.
     */
    public Properties(Properties defaults) {
        this.defaults = defaults;
    }

So `LocalFlowProcess#getConfigCopy()` and `LocalFlowProcess#copyConfig()` should be something like:

    Properties copyConfig = new Properties(config) ;
    copyConfig.putAll(config) ;
    return copyConfig ;

* In Hadoop mode:

In Hadoop mode, the implementation of `HadoopFlowProcess#getConfigCopy()` is:

    return new JobConf( jobConf );

but in this case the semantic is different from the local one: it creates a copy.

I have tested the changes and seems to work as I expected. I could be wrong anyway...