messager.c: fix memory overlap (fixes artefacts in scrolling text)

==363== Source and destination overlap in memcpy(0xa066240, 0xa0662b8, 240)
==363==    at 0x4C2B220: memcpy@@GLIBC_2.14 (mc_replace_strmem.c:838)
==363==    by 0x407D97: newline (messager.c:43)
==363==    by 0x407EE6: put (messager.c:54)
==363==    by 0x40806E: messager (messager.c:77)
==363==    by 0x403009: bb (bb.c:258)
==363==    by 0x407C06: main (main.c:202)

--- a/messager.c
+++ b/messager.c
@@ -40,8 +40,8 @@ static void newline()
 	start = 0;
     cursor_y++, cursor_x = 0;
     if (cursor_y >= aa_scrheight(context)) {
-	memcpy(context->textbuffer + start * aa_scrwidth(context), context->textbuffer + (start + 1) * aa_scrwidth(context), aa_scrwidth(context) * (aa_scrheight(context) - start - 1));
-	memcpy(context->attrbuffer + start * aa_scrwidth(context), context->attrbuffer + (start + 1) * aa_scrwidth(context), aa_scrwidth(context) * (aa_scrheight(context) - start - 1));
+	memmove(context->textbuffer + start * aa_scrwidth(context), context->textbuffer + (start + 1) * aa_scrwidth(context), aa_scrwidth(context) * (aa_scrheight(context) - start - 1));
+	memmove(context->attrbuffer + start * aa_scrwidth(context), context->attrbuffer + (start + 1) * aa_scrwidth(context), aa_scrwidth(context) * (aa_scrheight(context) - start - 1));
 	memset(context->textbuffer + aa_scrwidth(context) * (aa_scrheight(context) - 1), ' ', aa_scrwidth(context));
 	memset(context->attrbuffer + aa_scrwidth(context) * (aa_scrheight(context) - 1), 0, aa_scrwidth(context));
 	cursor_y--;