[RFE] Make 'svn patch' read from STDIN

I suggest to extend 'svn patch' so that it supports usage in a pipe like

    gzip -dc patch-0042.gz | svn patch -P patch-0042 -

This would permit using 'svn patch' directly as a drop-in replacement for

   gzip -dc patch-0042.gz | patch

An example use case is the '%autosetup -S [SCM]' feature of RPM
(http://www.rpm.org/wiki/PackagerDocs/Autosetup,introducedinversion4.11;
currently supported SCM are patch, git, hg, bzr, quilt). The pipe in the
'%autopatch' macro uses various decompressors and transfers the text output to
the 'SCM' command. It would be nice to permit '-S svn' here as well.