Tweak get-version to do the right thing with multiple head tags.

bld/get-version

@@ -8,6 +8,8 @@
 # which has a set of references substituted into it by git.
 # If we can find one which matches $v[0-9].* then we assume it's
 # a version-number tag, else we just use the whole string.
+# If there is more than one v[0-9].* tag, sort them and use the
+# first. This favours, eg v2.63 over 2.63rc6.
 
 if which git >/dev/null 2>&1 && [ -d $1/.git ]; then
      cd $1; git describe
@@ -18,7 +20,7 @@ else
      vers=`cat $1/VERSION | sed 's/[(), ]/,/ g' | tr ',' '\n' | grep $v[0-9]`
 
      if [ $? -eq 0 ]; then
-         echo "${vers}" | head -n 1 | sed 's/^v//'
+         echo "${vers}" | sort | head -n 1 | sed 's/^v//'
      else
          cat $1/VERSION
      fi