git-svn: lazy load some modules

We can delay loading some modules until we need them for uncommon
code paths.  For example, persistent memoization is not often
needed, so we can avoid loading the modules for it until we
encounter svn::mergeinfo during fetch.

This gives a tiny reduction in syscalls (from 15641 to 15305) when
running "git svn info" and counting via "strace -fc".  Further,
more invasive work will be needed to noticeably improve performance.

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

perl/Git/SVN/Editor.pm

@@ -5,7 +5,6 @@ use warnings;
 use SVN::Core;
 use SVN::Delta;
 use Carp qw/croak/;
-use IO::File;
 use Git qw/command command_oneline command_noisy command_output_pipe
            command_input_pipe command_close_pipe
            command_bidi_pipe command_close_bidi_pipe/;
@@ -586,7 +585,7 @@ The interface will change as git-svn evolves.
 =head1 DEPENDENCIES
 
 Subversion perl bindings,
-the core L<Carp> and L<IO::File> modules,
+the core L<Carp> module,
 and git's L<Git> helper module.
 
 C<Git::SVN::Editor> has not been tested using callers other than