svn improt needs SVN::Core 1.2.1 or better

Die with a warning if Perl's svn module is too old.

Signed-Off-By: Matthias Urlichs <smurf@smurf.noris.de>

git-svnimport.perl

@@ -26,6 +26,8 @@ use IPC::Open2;
 use SVN::Core;
 use SVN::Ra;
 
+die "Need CVN:COre 1.2.1 or better" if $SVN::Core::VERSION lt "1.2.1";
+
 $SIG{'PIPE'}="IGNORE";
 $ENV{'TZ'}="UTC";