Buildsystem: Clean up build-process on all platforms

- Windows: Use CMAKE_INSTALL_PREFIX as a 'final install' directory (thanks to paradox for the preload-handling)
  (New target INSTALL, -not- included as part of ALL_BUILD (must be specifically run for installation to start)
- All: Build libmpq library (used for tools)
- All: Build extractiontools with hardlinked mpq-library (no need to install it anymore)
- All: Move jemalloc from being harddefined to using a CMake string (fixes issue 3378) (thanks to tru.bazoozoo for the idea, alternative added)

--HG--
branch : trunk

externals/ace/CMakeLists.txt

@@ -335,3 +335,5 @@ add_library(ace SHARED ${ace_STAT_SRCS})
 if(PCH)
   add_native_precompiled_header(ace ${CMAKE_SOURCE_DIR}/externals/ace/PrecompiledHeaders/WinAcePCH)
 endif()
+
+install(TARGETS ace DESTINATION "${CMAKE_INSTALL_PREFIX}")