simplified file permission handling

This patch simpliefies the configuration of the file and directory creation
modes. There is no need to set the umask anymore. Only the wanted permissions
for files and directories are set. An init function compares the wanted modes
with the ones that would be choosen by the system automatically (consulting
the system's umask) and sets the modes for chmod when needed.

darcs-hash:20060304154038-7ad00-5ef1db3a87e42563a602f9d050c681d2ea74682f.gz