git-svn: fix symlink-to-file changes when using command-line svn 1.4.0

git-svn: fix symlink-to-file changes when using command-line svn 1.4.0

I incorrectly thought this was hopelessly broken in svn 1.4.0,
but now it's just broken in that the old method didn't work.  It
looks like svn propdel and svn propset must be used now and the
(imho) more obvious svn rm --force && svn add no longer works.

"make -C t full-svn-test" should now work.

Signed-off-by: Eric Wong <redacted>
Acked-by: Uwe Zeisberger <redacted>
Signed-off-by: Junio C Hamano <redacted>