Add regression test for lid-driven cavity flow.

 * Associated inputs are in the folder tests/NavierStokes.
 * Edit makefile appropriately.
 * Use function initialize for FlowDescription & SimulationParameters.
 * Change member permissions to public in the solver classes.
 * Edit .gitignore.
Edit the rule for running tests.

 * The rule now both compiles and runs the tests.
 * Add flag to compile c++0x to the makefile in src/solvers.