url: a short host name + port is not a scheme

The function identifying a leading "scheme" part of the URL considered a
few letters ending with a colon to be a scheme, making something like
"short:80" to become an unknown scheme instead of a short host name and
a port number.

Extended test 1560 to verify.

Also fixed test203 to use file_pwd to make it get the correct path on
windows. Removed test 2070 since it was a duplicate of 203.

Assisted-by: Marcel Raad
Reported-by: Hagai Auro
Fixes #3220
Fixes #3233
Closes #3223
Closes #3235