dvol support for `git branch <newbranch>'

[wallnerryan]

This is the error

-> dvol branch hiagain
Wrong number of arguments.

Expected behavior

-> dvol branch hiagain
->

[lukemarsden]

To be clear, you'd expect this to make a new branch from current branch's HEAD but not check it out?

Should be simple to add this, https://github.com/ClusterHQ/dvol/blob/master/voluminous/dvol.py#L438

add a parseArgs

def parseArgs(self, branch=None):
        self.branch = branch

then factor out https://github.com/ClusterHQ/dvol/blob/master/voluminous/dvol.py#L121 into a new function createBranch

then add to run something like

    if self.branch is not None:
        self.voluminous.createBranch(...)

anyone fancy picking this up as low hanging fruit?