Adds wrapping appender which adds process wide lock

[mfreiholz]

Ideas:

• Semaphores
• Lock file

Its currently only useful for all kind of FileAppenders, if multiple processes try to log into the same file.

[hsimpson]

On Windows you can use CreateMutex() with the name "Global\MyMutexName" to get a "global" mutex which is valid for more then on process. Suggestion add the executable name to the path name.