implement getting multiple nodes by uuid

[dbu]

adjust jackrabbit to be able to fetch multiple nodes by uuid, as we can by path now.
#34 adjusts the code to shift the responsibility to the transport.

@chregu can you provide your jackrabbit code here when you find it? if it does not exist, could you dig up the original patch you wrote for fetching multiple nodes by path? this one will look similar.

[dbu]

@chregu, would you still have this around?