[PATCH] Some infrastructure work for virtual file system (now on phab)

[Rafael Espíndola]

> And even worse, because RealFileSystem is an implementation detail, and
> getRealFileSystem returns a ref counted pointer by value, I cannot see any
> way to get me a RealFileSystem without locking.

Maybe we could use a plain point in here. As Douglas says, that would
"toss the responsibility for managing the FS instance up to “the
client”", but the only client that needs reference counting should be
libclang and it can do it with a non-intrusive counter wrapping the
pointer (like a shared_ptr).

Cheers,
Rafael