Fix a minor bug where if a role was granted the same capabilities through multiple menu items, the internal capability list would contain a bunch of arrays instead of simple boolean values. 

Note: As far as I know, this bug did not actually cause any issues in practice since PHP considers non-empty arrays "truthy". That is, both boolean `true` and `array(true, true, true)` behave the same in if statements. Still, it should be fixed for forward-compatibility reasons.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@803071 b8457f37-d9ea-0310-8a92-e5e31aec5664
Set "extra_capability" to null when the user sets it to an empty string in the "Permissions" window.

Fixes a recently introduced bug where opening the "Permissions" window for a menu item that did not have an extra capability and then clicking "Save Changes" in the window and the main editor screen (without making any changes) would add a new extra capability equal to the required capability. 

Cause: There's an  "extra_capability" editor field that's only used in the free version, but it is still present in the Pro version, just hidden. When you save the menu, the plugin re-reads the state of all menu properties from editor inputs (note: this is redundant since they're already updated on change), which happens to include the extra cap. field, which won't have the "this field is at the default setting" flag if extra capability = "".

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@804775 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add a compatibility workaround for Shopp 1.2.9.

Summary: Shopp adds an admin_menu hook while the admin_menu action is already running. As a result, AME does not see menu changes made by that Shopp hook. Priority settings do not apply if someone adds a new hook for action X while action X is running.

"Fixed" by making AME abuse the same behaviour - skip the first hook_admin_menu run and add a second run to the end of the admin_menu filter list.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@804872 b8457f37-d9ea-0310-8a92-e5e31aec5664