esc_url() mangles array format query variables in URLs

[johnbillion]

http://example.com/?test[foo]=bar is a valid URL, but esc_url() mangles it into http://example.com/?testfoo=bar.

To reproduce:

$url = 'http://example.com/?test[foo]=bar';

echo '<pre>';
var_dump( $url );
var_dump( esc_url( $url ) );
echo '</pre>';

Also affects array format query variables without named keys, eg. foo[]=bar.

Tested back to 3.4. May affect earlier versions.

[SergeyBiryukov]

Duplicate of #16859.