Description:
------------
Please see the test script. parse_url() is inconsistent with "//localhost:80/path"

Test script:
---------------
<?php
var_dump(parse_url('//localhost/path'));
var_dump(parse_url('//localhost:80/path'));
var_dump(parse_url('//localhost:/path'));
var_dump(parse_url('http://localhost:80/path'));

Expected result:
----------------
# //localhost/path
array(2) {
  ["host"]=>
  string(9) "localhost"
  ["path"]=>
  string(5) "/path"
}

# //localhost:80/path
array(2) {
  ["host"]=>
  string(9) "localhost"
  ["port"]=>
  int(80)
  ["path"]=>
  string(5) "/path"
}

# //localhost:/path
array(2) {
  ["host"]=>
  string(9) "localhost"
  ["path"]=>
  string(5) "/path"
}

# http://localhost:80/path
array(4) {
  ["scheme"]=>
  string(4) "http"
  ["host"]=>
  string(9) "localhost"
  ["port"]=>
  int(80)
  ["path"]=>
  string(5) "/path"
}

Actual result:
--------------
# //localhost/path
array(2) {
  ["host"]=>
  string(9) "localhost"
  ["path"]=>
  string(5) "/path"
}

# //localhost:80/path
bool(false)

# //localhost:/path
array(2) {
  ["host"]=>
  string(9) "localhost"
  ["path"]=>
  string(5) "/path"
}

# http://localhost:80/path
array(4) {
  ["scheme"]=>
  string(4) "http"
  ["host"]=>
  string(9) "localhost"
  ["port"]=>
  int(80)
  ["path"]=>
  string(5) "/path"
}