git-svn: reduce scope of input record separator change

git-svn: reduce scope of input record separator change

Reducing the scope of where we change the record separator ($/)
avoids bugs in calls which rely on the input record separator
further down, such as the 'chomp' usage in command_oneline.

This is necessary for a future change to git-svn, but exists in
Git.pm since it seems useful for gitweb and our other Perl
scripts, too.

Signed-off-by: Eric Wong <e@80x24.org>