When newvers.sh is run, it is possible that the svnversion
(or svnliteversion) in the current lookup path is not what
was used to check out the tree.  If an incompatible version
is used, the svn revision number is not reported in uname(1).

Run ${svnversion} on newvers.sh itself when evaluating if the
svn(1) in use is compatible with the tree.  Fallback to an
empty ${svnversion} if necessary.

With this change, svnliteversion from base is only used
if no compatible svnversion is found, so with this change,
the version of svn(1) from the ports tree is evaluated first.

Requested by:	many
MFC after:	3 days
X-MFC-To:	stable/9, releng/9.2 only
gpt_entries is used as limit for the number of partition entries in
the GEOM_PART. Instead of just using number of entries from the GPT
header, calculate this limit based on the reserved space between
GPT header and first available LBA.

MFC after:	2 weeks