Adding Travis build configuration

Travis has a funny GCC 4.6 build environment.  Supporting CMakeLists adjustments are necessary to ensure that everything links correctly.  These adjustments are innocuous overspecifications of libraries that would be required anyway, or genuine lapses that would create problems for gcc on certain platforms.
Attempting to speed up non-PCH builds
Enabling unit tests with CTest
Merge pull request #1 from leapmotion/feature-travis

Enable travis build system