Replace dirent with boost::filesystem

[shrijitsingh99]

As suggested in #2888, replaced dirent with boost::filesystem

[kunaltyagi]

With Boost, there's no need of keeping it exclusive to only non-Windows users

[shrijitsingh99]

With Boost, there's no need of keeping it exclusive to only non-Windows users

Done
None of these functions in file_io.hpp are covered by any of the tests. Is a test needed for them?

[taketwo]

You know, I'm skeptical about this entire file common/file_io.h. It provides tiny subset of boost::filesystem functionality. Do we need it? Both PCL and downstream projects should just use boost::filesystem directly.

[kunaltyagi]

It provides tiny subset of boost::filesystem functionality

This wouldn't be an issue if the interface was a bit better. I mean it's a bit of annoyance to iterate over a directory and check each file. Much better to have a nice interface which acts like a generic filter

for (const auto file: pcl::io::with_extension(pcl::io::get_readable_files("directory"), ".pcd"))
...

std::vector<std::string> files;
pcl::io::getAllPcdFilesInDirectory("directory", files);
for (const auto file: files)
...

Without these 10 lines, each project will have to reproduce this. And it has pitfalls, like extension() having a dot, file iterator giving broken symlinks, etc. which we can remove

[taketwo]

Much better to have a nice interface which acts like a generic filter

OK, I agree that in principle we can provide a nicer interface on top of boost::filesystem. (But this is not what is available in file_io.h at teh moment 😆 )