added 'append' property for FileAppender.
added 'append' property for FileAppender.

ksmyth/log4cpp,orocos-toolchain/log4cpp,orocos-toolchain/log4cpp,adobni/log4cpp,adobni/log4cpp,ksmyth/log4cpp,halex2005/log4cpp,iocroblab/log4cpp,halex2005/log4cpp,iocroblab/log4cpp,halex2005/log4cpp,adobni/log4cpp,iocroblab/log4cpp,ksmyth/log4cpp