Fix coverage data generation for coveralls.

- .travis.yml: Fix name of tests directory in
- Configuration: Add gcov library and other coverage flags to cmake, enable this
  in .travis.yml
- .travis.yml: Reduce default number of processes (4 processes crashed
  intermittently, presumably due to memory exhaustion on travis VM instance)
Enable pedantic flags for travis.

Also build with 3 processes and run tests with 4 processes (otherwise lcov runs
out of time).