[SAGA-RG] NSEntry constructor

[Roelof Kemp]

Hi Andre,

I have a few comments about the NSEntry. The notes of the constructor 
state that all notes from the open call (on ns_directory) apply.

* The notes of the open call specify an AlreadyExists exception which is 
not in the Throws list of the NSEntry constructor.
* It is not clear from the description of the ns_directory open call if 
it should create a new file if:
  1. The file does not exists
  2. The CREATE flag is set
  I think it should, is that true? If so, maybe you can add it to the 
postconditions.

Roelof