geo module adds tests even if dependencies aren't found

[Chris Hillery]

The geo module always calls ADD_TEST_DIRECTORY() on its test/ directory, without regards to whether libgeos was found. All those tests are run and fail if you don't have libgeos installed.

Assigning to Juan - I believe you were going to do some module-package splitting, so (as a relatively low priority) you should also split the geo module into separate geo and geoproj modules, each with appropriate dependency-checking for source and tests.