Make pressing the search button within an app that does not support

search bring up global search. This still respects the case where an
app has chosen to disable search entirely by overriding
onSearchRequested() to return false.

I do not believe any changes to the SearchManager documentation
(http://developer.android.com/reference/android/app/SearchManager.html#HowSearchIsInvoked)
are necessary, because this documentation already indicates that
pressing the search button within an app that does nothing special with
regard to search can bring up global search.