Supports colored output on term type screen-256color.

Proposed as a one-line patch by Tom Jakubowski (tom@crystae.net);
finished by Zhanyong Wan.

src/gtest.cc

@@ -204,7 +204,7 @@ GTEST_DEFINE_string_(
     "Whether to use colors in the output.  Valid values: yes, no, "
     "and auto.  'auto' means to use colors if the output is "
     "being sent to a terminal and the TERM environment variable "
-    "is set to xterm, xterm-color, xterm-256color, linux or cygwin.");
+    "is set to a terminal type that supports colors.");
 
 GTEST_DEFINE_string_(
     filter,
@@ -2497,6 +2497,7 @@ bool ShouldUseColor(bool stdout_is_tty) {
         String::CStringEquals(term, "xterm-color") ||
         String::CStringEquals(term, "xterm-256color") ||
         String::CStringEquals(term, "screen") ||
+        String::CStringEquals(term, "screen-256color") ||
         String::CStringEquals(term, "linux") ||
         String::CStringEquals(term, "cygwin");
     return stdout_is_tty && term_supports_color;

test/gtest_unittest.cc

@@ -6429,6 +6429,9 @@ TEST(ColoredOutputTest, UsesColorsWhenTermSupportsColors) {
   SetEnv("TERM", "screen");  // TERM supports colors.
   EXPECT_TRUE(ShouldUseColor(true));  // Stdout is a TTY.
 
+  SetEnv("TERM", "screen-256color");  // TERM supports colors.
+  EXPECT_TRUE(ShouldUseColor(true));  // Stdout is a TTY.
+
   SetEnv("TERM", "linux");  // TERM supports colors.
   EXPECT_TRUE(ShouldUseColor(true));  // Stdout is a TTY.