Patch release for 1.9.10 that improves the stability of the engine and fixes some incorrect behavior.

• Map Renderer: Secret exit switch coords in DOOM E3M6
• OpenAL: Compilation failure with integer conversion in 64-bit build
• Fatal exception about failure to get a lock (bug in de::Lockable)
• Handle exception if failed to open log output file (e.g., starting a second instance of Doomsday when running a dedicated server on the same machine)

• 1.9.10 release notes