url: Fix parsing for when 'file' is the default protocol

Follow-up to 3463408.

Prior to 3463408 file:// hostnames were silently stripped.

Prior to this commit it did not work when a schemeless url was used with
file as the default protocol.

Ref: https://curl.haxx.se/mail/lib-2016-11/0081.html
Closes https://github.com/curl/curl/pull/1124

Also fix for drive letters:

- Support --proto-default file c:/foo/bar.txt

- Support file://c:/foo/bar.txt

- Fail when a file:// drive letter is detected and not MSDOS/Windows.

Bug: https://github.com/curl/curl/issues/1187
Reported-by: Anatol Belski
Assisted-by: Anatol Belski

tests/data/test1534

@@ -27,7 +27,7 @@ http
 lib1534
 </tool>
 <name>
-Test CURLINFO_RESPONSE_CODE
+CURLINFO_FILETIME init and reset
 </name>
 <command>
 http://%HOSTIP:%HTTPPORT/1534