Use memmove instead of memcpy for overlapping areas

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/imap-send.c b/imap-send.c
index 16804ab..a6a6568 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -272,7 +272,7 @@
 				n = b->bytes - start;
 
 				if (n)
-					memcpy( b->buf, b->buf + start, n );
+					memmove(b->buf, b->buf + start, n);
 				b->offset -= start;
 				b->bytes = n;
 				start = 0;