t9010 (svn-fe): use Unix-style path in URI

t9010 (svn-fe): use Unix-style path in URI

Ever since v1.6.3-rc0~101^2~14 (Tests on Windows: $(pwd) must return
Windows-style paths, 2009-03-13), there is a subtle difference between
$(pwd) and $PWD in tests: the former returns Windows-style paths as
might be output by git and the latter Unix-style paths which msys
programs tend to prefer.

In file:// URIs, Unix-style paths are needed.  Before: “svn export”
declares it cannot find

 file://c:/apps/git/git/t/trash directory/simple-svco

After: “svn export” successfully finds

 file:///c/apps/git/git/...

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>