1. Express desired path.join behavior in tests.
2. Update fs.realpath to reflect new path.join behavior
3. Update url.resolve() to use new path.join behavior.
Note that "//" is still a special indicator for the hostname, and this does
not change the parsing of mailto: and other "slashless" url schemes. It
does however remove some oddness in url.parse(req.url) which is the most
common use-case for the url.parse function.
Also, make a slight change from original on url-module to put the
spacePattern into the function. On closer inspection, it turns out that the
nonlocal-var cost is higher than the compiling-a-regexp cost.
Also, documentation.
