Allow max names of 255 characters

[uli-heller]

This pull request fixes #391. For details related to the bug see there. For me, it seems to work quite well. I did NOT test it extensively. I just tried to create the debian package for GOCRYPTFS an this failed before due to issues related to file name length. Now it works.

In order to allow names of 255 characters, I extended most buffers from NAME_MAX to NAME_MAX+1. We probably use the buffers for null-terminated filenames, so we need 255 characters + the closing null byte.