use reliable event 'keydown' for detecting Tab key
fix remaining context menu when owner tooltip panel closes
fix disabled control when tooltip panel has focus
make module of event observer to cancel blinking by click
remove check for invisible link

* I deceded to remove it since an invisible link doesn't match with a
  navigation-like much and no harm if matches, and for better performance.
reduce max number of test links for navigation

* It seems to be enough for my use.
make named hash of navi words for readability
improve regexp values for navi-like sign and word
fall through URI object for plan of improving navi-link tester"
optimize parts of URL for comparison
improve navi link tester

* rename modules to clearer names.
* URL test: compare the path of the original URL and the path of the portion of
  the original URL in a target URL.