Do not expand globs in FileSystem.find

[mrzasa]

FileSystem.find was expanding globs causing subtle errors described in

• https://github.com/fakefs/fakefs/issues/264
• https://github.com/fakefs/fakefs/issues/423 files with special characters (* or {}) weren't found.

This PR addresses those problems. I've simplified FileSystem.find that it doesn't expand globs now. In case glob expansion is needed (as in Dir.glob), we can use FileSystem.find_with_glob which contains the old implementation of find (the one with glob expantion).

Fixes https://github.com/fakefs/fakefs/issues/264 Fixes https://github.com/fakefs/fakefs/issues/423

[grosser]

looks great, thx!

[grosser]

2.3.0