[javascript] fix test_ajax.js implementation
In cubicweb.ajax.js, we maintain two lists (cw.loaded_src and cw.loaded_href)
to keep track of already included CSS and JS. (see discussion about
jQuery and $('foo').appendTo($head) in _loadAjaxHtmlHead.)
Since all tests are executed in the "same page", those two
variables need to be reinitialized before each test.
###############################################################################
#
# Put here information about external resources / styles used by your cube,
# or to overides existing UI properties.
#
# Existing properties are available through the `sheet` dictionary available
# in the global namespace. You also have access to a `data` function which
# will return proper url for resources in the 'data' directory.
#
# /!\ this file should not be imported /!\
###############################################################################
# CSS stylesheets to include in HTML headers
# uncomment the line below to use template specific stylesheet
# STYLESHEETS = sheet['STYLESHEETS'] + [data('cubes.%(cubename)s.css')]