ops: epetra: revise overload constraints of norms

[mzuzek]

refs #450

Overloads

Epetra overloads of norms:

function	input	remarks
norm1 norm2	Epetra_Vector	requires underlying scalar type to be known integral of floating-point type

Tests

Unit tests (in tests/functional_small/ops/):

file name	test name	tested type
ops_epetra_vector.cc	ops_epetra.vector_norm1 ops_epetra.vector_norm2	Epetra_Vector