xseg: Add X_CREATE op and protocol entry

Extend XSEG protocol with the X_CREATE op and the associated request data.
python: update distribute_setup.py
xseg: Add contaddr_size field to xseg request
xseg: Add rename op and request struct
xseg: Add flags to map reply struct

Add flags to map reply struct.

Introduce a new ZERO flag to mark the zero objects introduced by mapper and do
not exist on the backend.
Merge PR #4 (feature-xcreate) from philipgian/libxseg into develop

This patch set adds support for two new xseg operations:
XCREATE and XRENAME.

It also adds the necessary fields to support the assume_v0
functionality for Archipelago.
xseg: Change posixfd directory permissions

Change '/run/shm/posixfd' directory permissions from '01755'
to '01777'. An ordinary user can now create/unlink his named
pipes.
Switch license to GPLv3

According to the decision of the GRNET Board of Directors,
switch license to GPLv3.

This commit will be propagated to the release
and master branches based on git flow, and the next
release will be licensed as GPLv3.