Add some functionality like scandir about filesystem

[Lastique]

I think this is better implemented on top of directory_iterator. scandir exists because C has rather limited standard library, in C++ you can simply do something like this:

std::set<path> paths;
std::copy_if(directory_iterator(dir), directory_iterator(), std::inserter(paths), filter);

[soroshsabz]

@Lastique Thanks for response, I think the main difference is performance, because in iterating, boost use readdir in internal implementation, and I think scandir is faster than readdir step by step for scanning usage.

[Lastique]

scandir is also most likely using readdir or the underlying syscall internally. See it in glibc for instance. I would say, using C++ tools for this has better potential performance because of more aggressive inlining, although the raw code performance is probably offset by readdir cost.