I added an additional invalid test which David pointed out and made changes to invalid url checking code. I moved it more higher level.

- The reason for doing this is, invalid url test code (which is very specific for '[' enclosed ']' ipv6 url is concentrated at a single place). We can deal with parsing separately from check.

Now, other forms of Invalid URLs are possible as David points out (and possibly more too), but leaving it is better as it would unnecessarily add syntax-checks at various different places (instead of a single place), without much of value add.  Dealing with Valid URLs and a parse logic checking should be fine.

commits: trunk - r80277 and py3k - r80278