CPP11 — Sequences and get_buffer()

Summary: This is a new issue for the C++ RTF.

The mapping for sequences mandates a get_buffer() accessor for read/write
access to the members of the sequence. It is mentioned that an implemen-
tation is not required to store sequence elements in continuous memory
for efficiency reasons, but may choose to do so only when get_buffer()
is called.

However, this introduces coherency problems if sequence elements are
accessed and modified using both get_buffer() and operator[].

get_buffer() is not possible for recursive sequences anyway.

Close no change. The submitter of the issue misread the specification.