#131 Verify if file could be opened in (Rolling)FileAppender

[lighto-kun]

I have noticed, that FileAppender does not seem to verify whether it could successfully open the file for writing or not. This is not nice, since it does not give me the means to react properly if the file could not be opened. There is an option (although not the best/clean) to open the file yourself and pass the filedescriptor to the FileAppender, but the similar interface is not provided by the RollingFileAppender, in case i want to use RollingFileAppender.

Additionally, im not sure if it is a good idea to use unix-specific functions open(...) and close(...) for file manipulations. Wouldn't the use of C++ standard library functions make the log4cpp more platform independent? It is just a thought.