git-svn: workaround a for broken symlinks in SVN

It's possible for bad clients to commit symlinks without the
5-character "link " prefix in symlinks.  So guard around this
bug in SVN and make a best effort to create symlinks if the
"link " prefix is missing.

More information on this SVN bug is described here:
  http://subversion.tigris.org/issues/show_bug.cgi?id=2692

To be pedantic, there is still a corner case that neither we nor
SVN can handle:  If somebody made a link using a broken SVN
client where "link " is the first part of its path, e.g.
"link sausage", then we'd end up having a symlink which points
to "sausage" because we incorrectly stripped the "link ".
Hopefully this hasn't happened in practice, but if it has,
it's not our fault SVN is broken :)

Thanks to Benoit Sigoure and Sverre Johansen for reporting
and feedback.

Signed-off-by: Eric Wong <normalperson@yhbt.net>

git-svn.perl

@@ -3177,9 +3177,15 @@ sub close_file {
 		}
 		sysseek($fh, 0, 0) or croak $!;
 		if ($fb->{mode_b} == 120000) {
+			eval {
 				sysread($fh, my $buf, 5) == 5 or croak $!;
 				$buf eq 'link ' or die "$path has mode 120000",
-			                       "but is not a link\n";
+						       " but is not a link";
+			};
+			if ($@) {
+				warn "$@\n";
+				sysseek($fh, 0, 0) or croak $!;
+			}
 		}
 		defined(my $pid = open my $out,'-|') or die "Can't fork: $!\n";
 		if (!$pid) {