make test runner IE-safe
don't run async pre-load tests if library loads before calls to identify/name_tag (rare race condition)
port lib-apidown implementation test from mixpanel repo
port lib-snippet test from mixpanel repo as lib-2implementations
deal with race conditions in 2implementations test setup: if the lib loads before the rest of the setup JS runs then skip pre-loading tests
implementation test for loading lib in head tag
implementation test for mixpanel calls in head tag
test calling all public API functions in head before lib loads
test that functions continue to work in head after lib loads
remove lib-headinit (superceded by lib-headcalls)
test for setting api_host to https in init callback
tests for lib functionality when cookie-setting fails
add warning to page when async-tracking tests are skipped due to lib loading too quickly
ensure that post-load tests run even if 'loaded' callback doesn't fire because lib is already loaded
comment to explain kicking off test_mixpanel() even when async tests get skipped
change global ref to instance in implementation test
remove pointless var check in test
reverse 'api down' test logic according to @ttrefren's suggestion
add headcalls test to ensure that lib loads successfully
fix referrer redirect in headcalls test