Merge branch 'jc/svn-auth-providers-unusable-at-1.6.12'

Regression fix for people with libsvn between 1.6.12 and 1.6.15, on
which we tried to use the non-working platform auth providers.

* jc/svn-auth-providers-unusable-at-1.6.12:
  git-svn: platform auth providers are working only on 1.6.15 or newer

Author: gitster

git-svn.perl

@@ -4837,7 +4837,7 @@ ()
 
 	# earlier 1.6.x versions would segfault, and <= 1.5.x didn't have
 	# this function
-	if (::compare_svn_version('1.6.12') > 0) {
+	if (::compare_svn_version('1.6.15') >= 0) {
 		my $config = SVN::Core::config_get_config($config_dir);
 		my ($p, @a);
 		# config_get_config returns all config files from