Progress: Wrap up most of the directory do related changes in Featureless Make.

Progress: Wrap up most of the directory do related changes in Featureless Make.

I am hoping this is the last progress on Featureless Make to get it fully up to date with all of the changes.
While I won't be surprised if I missed something this feels like its ready.

Remove the directory recurse copy flags.

Use more caches in Featureless Make.
Move the directory do as a cache to better allow for reusing the path and path_custom strings.
Update the documentation comments regarding the caching.

The regression mentioned in commit 61a348ba714e41467da803f8220a31c126581a01 is resolved.
The regression is that I appended the path separator out of scope (outside of a relevant condition check).

I noticed another regression where when source.used is 0 the action is not performed.
This is incorrect because the source may be 0 and the paths being used are just relative paths.

Fix a mistake where the f_file_copy() and f_file_clone() are passed invalid flags.
Make sure to pass the appropriate flags to the f_file_clone() calls in the directory do handle callback.