FullPath.DirAndName() and FullPath.Name() used filepath.Split, which is
OS-dependent: on Windows it treats backslash as a path separator,
corrupting filer paths that contain literal backslashes. Filer paths
always use "/" as the separator, so switch to path.Split and path.Join
which only split on "/" regardless of the host OS.
This fixes the backslash case from #11243 where a file saved as
/test/special\reverseslash4.jpg was stored with a corrupted path on
Windows filer builds. The #, ?, and % cases from the same issue are
client-side URL-encoding problems (the server never receives the raw
characters), but once the client properly percent-encodes them the
server now handles the decoded path correctly on all platforms.
Chris Lu
01fc31cb71