git svn: read global+system config for clone+init

Since $GIT_DIR does not exist when initializing new repositories,
we can follow back to the global and system config files for
git.

The logic for this was originally introduced when
$GIT_DIR/config was the only config file git could read (back
when "git config" was "git repo-config"), so the function is
renamed to "read_git_config" instead of "read_repo_config".

Signed-off-by: Eric Wong <normalperson@yhbt.net>
diff --git a/git-svn.perl b/git-svn.perl
index 27fbe30..ea922ac 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -274,7 +274,7 @@
 
 my %opts = %{$cmd{$cmd}->[2]} if (defined $cmd);
 
-read_repo_config(\%opts);
+read_git_config(\%opts);
 if ($cmd && ($cmd eq 'log' || $cmd eq 'blame')) {
 	Getopt::Long::Configure('pass_through');
 }
@@ -1390,8 +1390,7 @@
 }
 
 # convert GetOpt::Long specs for use by git-config
-sub read_repo_config {
-	return unless -d $ENV{GIT_DIR};
+sub read_git_config {
 	my $opts = shift;
 	my @config_only;
 	foreach my $o (keys %$opts) {