Some improvement in building for unknown systems.

CMakeLists.txt

@@ -179,6 +179,17 @@ IF(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
 	MESSAGE(STATUS "Configuring for Solaris")
 ENDIF(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
 
+IF(NOT ETC_PREFIX)
+	IF(CMAKE_INSTALL_PREFIX)
+		MESSAGE(WARNING "Your system is unknown for rspamd, assume defining ETC_PREFIX and MAN_PREFIX by -D option, now ETC_PREFIX and MAN_PREFIX are relative to ${CMAKE_INSTALL_PREFIX}")
+		SET(ETC_PREFIX "${CMAKE_INSTALL_PREFIX}/etc")
+		SET(MAN_PREFIX "${CMAKE_INSTALL_PREFIX}/man")
+	ELSE(CMAKE_INSTALL_PREFIX)
+		MESSAGE(FATAL_ERROR "Your system is unknown for rspamd and no CMAKE_INSTALL_PREFIX specified, assume defining CMAKE_INSTALL_PREFIX")
+	ENDIF(CMAKE_INSTALL_PREFIX) 
+	MESSAGE(STATUS "Configuring for ${CMAKE_SYSTEM_NAME}")
+ENDIF(NOT ETC_PREFIX)
+
 INCLUDE(FindLua51)
 # Check for luajit
 IF(ENABLE_LUAJIT MATCHES "ON")