License review of data samples and docs

[robe]

review data samples used in docs and regression tests and note in license.txt documentation license and any associated licenses with the data used:

Jody Garnette suggested something like this: Moving forward in the docs we'll also try to note where data is gotten from (will add that to our code review section)

So if you had an entry about the docs you could say:
- creative commons license
- dataset xxxx from US Census Tiger data
- data or snapshots generated by community
- raster example from xxxx

[robe]

I've updated license.txt to be detail the documentation license and data. at r8311

[strk]

All done. PostGIS graduated.