Fix an abort observed on MacOS X 10.9 (but applicable to other platforms).

mapped_v4_to_regular_v4() committed the sin of doing strcpy(3) on
overlapping buffers.  This caused an abort on MacOS X 10.9.  Fix this
to use memcpy(3) instead, which handles overlapping buffers correctly.

Fixes #135 (Crash on OS X when using IP address)
(cherry picked from commit 723f2f7b2aed8ee06f081575bd888751f556b5d7)
Signed-off-by: Bruce A. Mah <bmah@es.net>