Add option to install newer libstdc++ on OS X

Also include a bzipped copy of libstdc++.6.dylib
Fixes #437
Fixes #436
Fixes #460
Fixes #462

library/CMakeLists.txt

@@ -306,6 +306,12 @@ IF(UNIX)
                 DESTINATION .)
         install(PROGRAMS ${dfhack_SOURCE_DIR}/package/darwin/dfhack-run
                 DESTINATION .)
+        OPTION(INSTALL_NEW_LIBSTDCXX "Install a version of libstdc++ from GCC 4.5.4 to fix various crashes" ON)
+        IF(INSTALL_NEW_LIBSTDCXX)
+            execute_process(COMMAND bunzip2 --keep --force ${dfhack_SOURCE_DIR}/package/darwin/libstdc++.6.dylib.bz2)
+            install(PROGRAMS ${dfhack_SOURCE_DIR}/package/darwin/libstdc++.6.dylib
+                DESTINATION ./hack/)
+        ENDIF(INSTALL_NEW_LIBSTDCXX)
     else()
         # On linux, copy our version of the df launch script which sets LD_PRELOAD
         install(PROGRAMS ${dfhack_SOURCE_DIR}/package/linux/dfhack