Win32: enable color output in Windows cmd.exe

Git requires the TERM environment variable to be set for all color*
settings. Simulate the TERM variable if it is not set (default on Windows).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -2113,6 +2113,10 @@ void mingw_startup()
 			setenv("TMPDIR", tmp, 1);
 	}
 
+	/* simulate TERM to enable auto-color (see color.c) */
+	if (!getenv("TERM"))
+		setenv("TERM", "cygwin", 1);
+
 	/* initialize critical section for waitpid pinfo_t list */
 	InitializeCriticalSection(&pinfo_cs);