This adds a check that triggers an error if Select2 was not able
to detect a copy of jQuery on the page. This should help users when
they are setting up Select2.
**Breaking change:** The full build no longer includes jQuery.
Previously, the full build included all requirements for Select2,
including jQuery, which meant that anyone looking for the optional
requirements had to possibly include multiple versions of jQuery
on their page. This means that anyone requiring Select2 to also
bundle jQuery will now need to include jQuery on their pages
alongside Select2. A copy of jQuery is included in the repository.
**Breaking change:** The AMD build of Select2 will now correctly
wrap the code in a `define` block. It will still create the named
blocks inside of the code, which should be valid in most AMD build
systems, so now Select2 is compatible with cases where the file
does not have the same name as the Select2 module name.
**Breaking change:** Select2 will re-use the AMD methods if they
are available on the page, but it will not longer leak the included
AMD loader to the global scope. The AMD methods will still be
available on the `jQuery.fn.select2.amd` namespace.
The `mock.js` test file has been renamed to `helpers.js` and will
handle the escalation of the `require` and `define` variables to
the global scope. It should be included in all test files, or the
tests will fail.
This closes https://github.com/select2/select2/issues/2946.
