Relax invalid url detection

We accept any url that urlparse accepts, provided
it has a scheme.

packaging/requirements.py

@@ -112,15 +112,10 @@ def __init__(self, requirement_string):
         self.name = req.name
         if req.url:
             parsed_url = urlparse.urlparse(req.url)
-            if parsed_url.scheme and "+" in parsed_url.scheme:
-                # VCS url
-                pass
-            elif parsed_url.scheme == "file":
+            if parsed_url.scheme == "file":
                 if urlparse.urlunparse(parsed_url) != req.url:
                     raise InvalidRequirement("Invalid URL given")
-            elif not (parsed_url.scheme and parsed_url.netloc) or (
-                not parsed_url.scheme and not parsed_url.netloc
-            ):
+            elif not parsed_url.scheme:
                 raise InvalidRequirement("Invalid URL: {0}".format(req.url))
             self.url = req.url
         else:

tests/test_requirements.py

@@ -104,9 +104,9 @@ def test_url_and_marker(self):
 
     def test_invalid_url(self):
         with pytest.raises(InvalidRequirement) as e:
-            Requirement("name @ gopher:/foo/com")
+            Requirement("name @ /a/b")
         assert "Invalid URL: " in str(e.value)
-        assert "gopher:/foo/com" in str(e.value)
+        assert "/a/b" in str(e.value)
 
     def test_file_url(self):
         req = Requirement("name @ file:///absolute/path")