nfv?asprintf are broken without va_copy, workaround them.

* drop nfasprintf.
* move nfvasprintf into imap-send.c back, and let it work on a 8k buffer,
  and die() in case of overflow. It should be enough for imap commands, if
  someone cares about imap-send, he's welcomed to fix it properly.
* replace nfvasprintf use in merge-recursive with a copy of the strbuf_addf
  logic, it's one place, we'll live with it.
  To ease the change, output_buffer string list is replaced with a strbuf ;)
* rework trace.c to call vsnprintf itself.  It's used to format strerror()s
  and git command names, it should never be more than a few octets long, let
  it work on a 8k static buffer with vsnprintf or die loudly.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>

imap-send.c

@@ -105,6 +105,19 @@ static void free_generic_messages( message_t * );
 
 static int nfsnprintf( char *buf, int blen, const char *fmt, ... );
 
+static int nfvasprintf(char **strp, const char *fmt, va_list ap)
+{
+	int len;
+	char tmp[8192];
+
+	len = vsnprintf(tmp, sizeof(tmp), fmt, ap);
+	if (len < 0)
+		die("Fatal: Out of memory\n");
+	if (len >= sizeof(tmp))
+		die("imap command overflow !\n");
+	*strp = xmemdupz(tmp, len);
+	return len;
+}
 
 static void arc4_init( void );
 static unsigned char arc4_getbyte( void );