web--browse: fix Mac OS X GUI detection for 10.6

Since OS X 10.6 the variable $SECURITYSESSIONID does not exist anymore,
so lets look for the $TERM_PROGRAM variable as backup.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-web--browse.sh

@@ -111,7 +111,8 @@ if test -z "$browser" ; then
 	browser_candidates="w3m links lynx"
     fi
     # SECURITYSESSIONID indicates an OS X GUI login session
-    if test -n "$SECURITYSESSIONID"; then
+    if test -n "$SECURITYSESSIONID" \
+	    -o "$TERM_PROGRAM" = "Apple_Terminal" ; then
 	browser_candidates="open $browser_candidates"
     fi
     # /bin/start indicates MinGW