Automatically set C4COPYRIGHT_YEAR on Linux [patch by Jookia]

Version.txt

@@ -7,7 +7,14 @@ SET(C4PROJECT           "OpenClonk Project")
 SET(C4PROJECT_DOMAIN    "openclonk")
 SET(C4PROJECT_TLD       "org")
 SET(C4PROJECT_URL       "http://www.{C4PROJECT_DOMAIN}.{C4PROJECT_TLD}")
-SET(C4COPYRIGHT_YEAR    2010) # Gimme CMAKE_CURRENT_YEAR already...
+
+IF(UNIX)
+	EXECUTE_PROCESS(COMMAND "date" "+%Y" OUTPUT_VARIABLE DATE)
+	STRING(REGEX REPLACE "(.+)\n" "\\1" YEARFIXED "${DATE}")
+	SET(C4COPYRIGHT_YEAR ${YEARFIXED})
+ELSEIF(WIN32)
+	SET(C4COPYRIGHT_YEAR "2011")
+ENDIF()
 
 SET(C4ENGINENAME        "OpenClonk")
 SET(C4ENGINENICK        "openclonk")