Test for correct handling of "download" attribute

These tests currently fail as there is no special treatment for this kind of
attribute.

Related: GH-1337
Support minimizable, non-boolean attributes

Fixes GH-1337
Rename CAN_BE_MINIMIZED to HAS_BOOLEANISH_VALUE
Combine valid value checks
Test more falsey values
meta http-equiv attribute name
Update refs example code to use onChange

Fixes #1408.

Test Plan: Copy each code snippet into jsbin; type in the text box successfully; click the button and see the input clear (and in the second example, get focused).
Fix preposition capitalization
Merge pull request #1183 from lrowe/patch-6

meta http-equiv attribute name
Fix PropType for travis

closes #1404
Rename "booleanish" to "overloaded boolean"
Don't try to detach a detached node

Test Plan: grunt test
Merge pull request #1410 from spicyj/sih

Don't try to detach a detached node
Match `setTimeout` delay with documentation
Merge pull request #1412 from gasi/patch-3

Match `setTimeout` delay with documentation
Merge pull request #1340 from matthewwithanm/download-attribute

Support download attribute properly