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