user can pass normal BCs to ReducedEquation

As things were before this MR, the user had to pass functions to ReducedEquation.__init__ that apply the BCs, instead of passing the BCs themselves. This is not necessary; instead, we can define

def _default_apply_bc(bc, u):
    if hasattr(u, "vector"):
        bc.apply(u.vector())
    else:
        bc.apply(u)
    return u

and

def _is_valid_bc(bc):
    return hasattr(bc, "apply")

and do

def __init__(self, reduced_function, bcs=None, h_bcs=None):
        bcs = [] if bcs is None else Enlist(bcs)
        h_bcs = [] if h_bcs is None else Enlist(h_bcs)

        bcs, h_bcs = self._validate_arguments(reduced_function, bcs, h_bcs)

        self.reduced_function = reduced_function
        self.bcs = bcs
        self.h_bcs = h_bcs

where _validate_arguments is defined as

def _validate_arguments(self, reduced_function, bcs, h_bcs):

        if not isinstance(reduced_function, ReducedFunction):
            raise TypeError("reduced_function should be a ReducedFunction")

        for i, bc in enumerate(bcs):
            if not callable(bc):
                if not _is_valid_bc(bc):
                    raise TypeError("Boundary conditions must have an 'apply' method!")
                else:
                    bcs[i] = partial(_default_apply_bc, bc)

        for i, h_bc in enumerate(h_bcs):
            if not callable(bc):
                if not _is_valid_bc(h_bc):
                    raise TypeError("Boundary conditions must have an 'apply' method!")
                else:
                    h_bcs[i] = partial(_default_apply_bc, h_bc)

        return bcs, h_bcs