Add Support for Session.getNode(String), .getProperty(String), and .removeItem(String)

JCR 2.0 requires some additional convenience methods on Session for retrieving nodes or properties (as opposed to Session.getItem(String), which does double duty), removing them, and checking for their existence. The method names are fairly self-documenting and are:

• getNode(String absPath)
• getProperty(String absPath)
• nodeExists(String absPath)
• propertyExists(String absPath)
• removeItem(String absPath)