create L.WMS even in AMD?

[sheppard]

Currently L.WMS is only assigned when using Leaflet as a global, so you can't do this:

define(['leaflet', 'leaflet.wms'], function(L) {
    var source = L.WMS.source(...);
});

Instead you have to do this:

define(['leaflet', 'leaflet.wms'], function(L, wms) {
    var source = wms.source(...);
});

It might be less confusing (and more consistent with other plugins) to support both options when running in AMD.