Attaching the patch to fix this issue. I deliberated upon this for a
while and came up with the approach to:

1) fix the port issue, wherein urlparse should technically recognize the 
':' separator for port from ':' after scheme.

2) And Doc fix wherein, it is advised that in the absence of a scheme,
use the net_loc as //net_loc (following RCF 1808).

If we go for any other fix, like internally pre-pending // when user has
not specified the scheme (like in many pratical purpose), then we stand
at chance of breaking a number of tests ( cases where url is 'g'(path
only),';x' (path with params) and cases where relative url is g:h)

Let me know your thoughts on this.

>>> urlparse('1.2.3.4:80')
ParseResult(scheme='', netloc='', path='1.2.3.4:80', params='',
query='', fragment='')
>>> urlparse('http://www.python.org:80/~guido/foo?query#fun')
ParseResult(scheme='http', netloc='www.python.org:80',
path='/~guido/foo', params='', query='query', fragment='fun')
>>>