Prevent tooltip content clicks from falling through

[jng]

Reported here:

​http://osgeo-org.1560.x6.nabble.com/Select-Object-by-clicking-with-select-tool-in-an-tooltip-in-the-ajax-viewer-td5359917.html

We need to prevent clicks inside tooltip content from propagating through to normal clicks on the map.

[jng]

In 9375:

Prevent clicks from tooltip content from falling through, triggering normal click handling (eg. Selection).

Fixes #2779

[jng]

In 9376:

Merged revision(s) 9375 from trunk/MgDev:
Prevent clicks from tooltip content from falling through, triggering normal click handling (eg. Selection).

Fixes #2779
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