Improve the version numbers generated by the build system

If we can't find a better date to use, then use today's date.

aclocal.m4

@@ -1551,6 +1551,15 @@ if test "$RELEASE" = "NO"; then
         AC_MSG_RESULT(given $PACKAGE_VERSION)
     else
         AC_MSG_WARN([cannot determine snapshot version: no .git directory and no VERSION file])
+        dnl We'd really rather this case didn't happenm but it might
+        dnl do (in particular, people using lndir trees may find that
+        dnl the build system can't find any other date). If it does
+        dnl happen, then we use the current date.
+        dnl This way we get some idea about how recent a build is.
+        dnl It also means that packages built for 2 different builds
+        dnl will probably use different version numbers, so things are
+        dnl less likely to go wrong.
+        PACKAGE_VERSION=${PACKAGE_VERSION}.`date +%Y%m%d`
     fi
 fi