Core htmx AJAX headers

• should handle HX-Retarget override back to this9ms ‣

  this.server.respondWith('GET', '/test', [200, { 'HX-Retarget': 'this' }, 'Result'])
  var div1 = make('<div id="d1" hx-get="/test" hx-target="#d2"></div>')
  var div2 = make('<div id="d2"></div>')
  div1.click()
  this.server.respond()
  div1.innerHTML.should.equal('Result')
  div2.innerHTML.should.equal('')