Extract some utilities from git-svn to allow extracting Git::SVN.

Put them in a new module called Git::SVN::Utils.  Yeah, not terribly
original and it will be a dumping ground.  But its better than having
them in the main git-svn program.  At least they can be documented
and tested.

* fatal() is used by many classes.
* Change the $can_compress lexical into a function.

This should be enough to extract Git::SVN.

Signed-off-by: Michael G. Schwern <schwern@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>

t/Git-SVN/Utils/can_compress.t

@@ -0,0 +1,11 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+use Test::More 'no_plan';
+
+use Git::SVN::Utils qw(can_compress);
+
+# !! is the "convert this to boolean" operator.
+is !!can_compress(), !!eval { require Compress::Zlib };