query strings with a forward slash give add_query_arg() problems

[markjaquith]

echo remove_query_arg('preview', 'p=16&preview=true/');

Expected result:

p=16

Actual result:

p=16&preview=true/

add_query_arg() is checking for a forward slash in the passed $uri. If present, it is assumed that $uri is a base with an empty query string, instead of being a pure query string.

[markjaquith]

(In [6030]) Require a slash AND the absence of an equals sign to designate the passed $uri as a base (without a query string). fixes #4903 for trunk

[markjaquith]

(In [6031]) Actually, let's just drop that slash check altogether. Equals sign is the best indicator. fixes #4903 for trunk

[nacin]

In 1192/tests:

Test add_query_arg() when used with only a query string. see #4903. see #23284.