When ReadDirPlus is enabled, the FUSE fs has to gather a lot of additional data for every file even if it won't be used (for example when the user is doing and 'ls' or a large glob). This can cause performance problems, so it should be possible to switch to the simple ReadDir behavior for file systems where this is a bottleneck.

Change-Id: I7f2e58fe6e728a408044ce789633423f6e527554