Git.pm: call tempfile from File::Temp as a regular function

We call File::Temp's "tempfile" function as a class method, but it was never designed to be called this way. Older versions seemed to tolerate it, but as of File::Temp 0.23, it blows up like this: $ git svn fetch 'tempfile' can't be called as a method at .../Git.pm line 1117. Fix it by calling it as a regular function, just inside the File::Temp namespace. Signed-off-by: H. Merijn Brand <h.m.brand@xs4all.nl> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>