recv_sideband: Do not use ANSI escape sequence on dumb terminals.

The "clear to end of line" sequence is used to nicely output the progress
indicator without leaving garbage on the terminal. However, this works
only on ANSI capable terminals. We use the same check as in color.c to
find out whether the terminal supports this feature and use a workaround
(a few spaces in a row) if it does not.

[jc: as an old fashoned git myself, and given the fact that the
possible prefix and suffix are small number of short constant strings,
I actually prefer a simpler-and-more-stupid approach.  This is with
Nico's clean-up.]
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sideband.c

@@ -13,14 +13,27 @@
  */
 
 #define PREFIX "remote:"
-#define SUFFIX "\033[K"  /* change to "        " if ANSI sequences don't work */
+
+#define ANSI_SUFFIX "\033[K"
+#define DUMB_SUFFIX "        "
+
+#define FIX_SIZE 10  /* large enough for any of the above */
 
 int recv_sideband(const char *me, int in_stream, int out, int err)
 {
 	unsigned pf = strlen(PREFIX);
-	unsigned sf = strlen(SUFFIX);
-	char buf[pf + LARGE_PACKET_MAX + sf + 1];
+	unsigned sf;
+	char buf[LARGE_PACKET_MAX + 2*FIX_SIZE];
+	char *suffix, *term;
+
 	memcpy(buf, PREFIX, pf);
+	term = getenv("TERM");
+	if (term && strcmp(term, "dumb"))
+		suffix = ANSI_SUFFIX;
+	else
+		suffix = DUMB_SUFFIX;
+	sf = strlen(suffix);
+
 	while (1) {
 		int band, len;
 		len = packet_read_line(in_stream, buf + pf, LARGE_PACKET_MAX);
@@ -59,10 +72,10 @@ int recv_sideband(const char *me, int in_stream, int out, int err)
 				 * line data actually contains something.
 				 */
 				if (brk > pf+1 + 1) {
-					char save[sf];
+					char save[FIX_SIZE];
 					memcpy(save, buf + brk, sf);
 					buf[brk + sf - 1] = buf[brk - 1];
-					memcpy(buf + brk - 1, SUFFIX, sf);
+					memcpy(buf + brk - 1, suffix, sf);
 					safe_write(err, buf, brk + sf);
 					memcpy(buf + brk, save, sf);
 				} else