From now on the betas will be numbered for the version that they will
become, so:
v1.53.0-beta.NNNN.CCCCC
Where N is commit number and C is commit. When released this will
become v1.53.0 and the beta will become v1.54.0-beta.NNN.CCCCC.
The commit number is the count of the commits since the root of the
tree since we can no longer use the the git version numbers since the
last tag.
This will simplify building the stable branch but that release
procedure hasn't been revised yet.
This commit also injects the name of the branch for the beta builds
into the download path.
Prior to this beta releases would appear to be older than the point
release, eg v1.49.0-096-gc41812fc which was released after v1.49.3 and
contains all the patches from v1.49.3.
Nick Craig-Wood