CMake: attempt to fix Boost detection on Fedora 20, which omits -mt.

CMakeLists.txt

@@ -741,6 +741,13 @@ if(UNIX AND NOT APPLE)
 				list(APPEND __boost_packages serialization)
 			endif()
 			find_package(Boost 1.48 COMPONENTS ${__boost_packages})
+			if(NOT Boost_FOUND)
+				# try to find non-multithreaded if -mt not found, this flag
+				# doesn't matter for us, it has nothing to do with thread
+				# safety, but keep it to not disturb build setups
+				set(Boost_USE_MULTITHREADED OFF)
+				find_package(Boost 1.48 COMPONENTS ${__boost_packages})
+			endif()
 			unset(__boost_packages)
 			if(Boost_USE_STATIC_LIBS AND WITH_BOOST_ICU)
 				find_package(IcuLinux)