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ARROW-1274: [C++] Fix CMake >= 3.3 warning. Also add option to suppress ExternalProject output

The default is the current behavior, but if enabled the build output will log ExternalProject build progress to files instead of dumping everything to the console. It might be nice to change the default to ON but we could do that in a separate patch

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #891 from wesm/ARROW-1274 and squashes the following commits:

a43d4e8 [Wes McKinney] Set verbose externalproject logging to true
10f8e92 [Wes McKinney] Fix CMake >= 3.3 warning. Also add option for verbose ExternalProject logging, otherwise suppress