Try to avoid readDir where pathExists may suffice

[roberth]

@grahamc

it looks like if the gitignore lib used builtins.pathExists instead of readDir to find .gitignore and .git dir entries, it would be much more optimally performant with lorri
since it uses readDir we effectively have to trigger new evaluations any time the list of files in a directory changes
whereas a pathExists call we can be much more precise about the watch behavior

Most of the IO there is written with memoization in mind
I don't see a reason right now why we can't do a pathExists before some readDirs so that seems worthwhile to investigate

[roberth]

@Profpatsch @grahamc I was able to eliminate some readDirs, see #33

Could you check whether this solves the problem?

[Profpatsch]

@curiousleo says he can’t reproduce: target/lorri#245 (comment)

update: he can’t reproduce even before this change. I’ll take a look.