Handle bcf_*_vector_end  - DO NOT MERGE YET

1. Modified SharedFieldIterator and IndividualFieldValueIterator to handle bcf_*_vector_end values. This is done by passing the end value of
the pointer in the constructor and modifying the "==" operator of the
iterator. The idea is that 2 iterators x,y are equal iff
 (a) x and y are identical  OR
 (b) (x == end && *y == bcf_*_vector_end) || (y == end && *x == bcf_*_vector_end)
2. Inserted test case fields for variable length vectors
That's a bug from my side.
The master branch defines the operator[] for an iterator as an offset from the original ptr (m_original_data_ptr). Is the intentional?
iter = m.begin()
iter++;
iter[0] 
iter[0] would still return the first element of the vector ( *(m.begin())  ), Is the what is expected?