Cached list of un-aliased paths is incorrect in drupal_lookup_path()

Problem/Motivation

The code to determine the list of un-aliased paths in drupal_lookup_path() is:

$cache['no_aliases'][$path_language] = array_flip(array_diff_key($cache['system_paths'], array_keys($cache['map'][$path_language])));

Given the following path arrays:

$cache[system_paths] ==>
Array
(
    [0] => node/1
    [1] => node/2
    [2] => node/3
    [3] => node/4
    [4] => node/5
    [5] => user/2/edit
    [6] => /user/logout
    [7] => taxonomy/term/1
    [8] => taxonomy/term/2
    [9] => taxonomy/term/3
    [10] => taxonomy/term/4
    [11] => taxonomy/term/5
)
$cache[map][$path_language] ==>
Array
(
    [node/1] => node-1
    [taxonomy/term/1] => taxonomy-term-1
    [taxonomy/term/2] => taxonomy-term-2
    [taxonomy/term/3] => taxonomy-term-3
)

the above code has the un-aliased list as:

$cache[no_aliases][$path_language] ==>
Array
(
    [node/5] => 4
    [user/2/edit] => 5
    [/user/logout] => 6
    [taxonomy/term/1] => 7
    [taxonomy/term/2] => 8
    [taxonomy/term/3] => 9
    [taxonomy/term/4] => 10
    [taxonomy/term/5] => 11
)

when in fact the list should be:

$cache[no_aliases][$path_language] ==>
Array
(
    [node/2] => 1
    [node/3] => 2
    [node/4] => 3
    [node/5] => 4
    [user/2/edit] => 5
    [/user/logout] => 6
    [taxonomy/term/4] => 10
    [taxonomy/term/5] => 11
)

Proposed resolution

Fix the expression by replacing array_diff_key() with array_diff().

Remaining tasks

Review and test.

User interface changes

None.

API changes

None.