SCP: relative path didn't work

When prefixing a path with /~/ it is supposed to be used relative to the
user's home directory but it didn't work. Now we cut off the entire
three byte sequenct "/~/" which seems to be how OpenSSH does it.

Bug: http://curl.haxx.se/bug/view.cgi?id=1173
Reported by: Balaji Parasuram