fixedFluxPressure BC: the snGrad is now pushed into the BC from pEqn.H rather than being evaluated in the BC

including two simple tutorial cases

This reverts commit c5bea524.

This reverts commit b18f6cc1.

Exception: applyWallFunctionBoundaryConditions.C cannot split #include
directives.

uniformDimensionedVectorField.

- change system/controlDict to use functions {..} instead of functions (..);
  * This is internally more efficient
- fixed formatting of system/controlDict functions entry

- pedantic change: use 'return 0' instead of 'return(0)' in the applications,
  since return is a C/C++ keyword, not a function.