FTP adapter cannot manage long paths

[FaustineLarmagna]

If a file or directory has a too long path the FTP adapter can't deal with it. The path is truncated and therefore the different FTP adapter's functions won't work (this results in a "file not found" type of PHP error).
I made a pull request of the solution I used to fix this: #430
This solution is currently used by a major player in the e-commerce sector in Europe.