Don't stomp on existing CZML DataSource name

If a CZML document does not define a name, it generates one from the
provided source URI.  However, it shouldn't generate a name if one
has already been provided via the constructor.
Merge pull request #2119 from AnalyticalGraphicsInc/czml-name-stomping

Don't stomp on existing CZML DataSource name
Fix #2050 by moving a clamp around in a shader.  Because drivers.
Merge pull request #2121 from AnalyticalGraphicsInc/issue2050

Fix #2050 by moving a clamp around in a shader.  Because drivers.
Merge remote-tracking branch 'origin/master' into oit-flag
Add unit tests.