fix symlink problems

[avikchaudhuri]

Re-implement the function dir.files that walks directories to collect files.

The main change is that when stat problems are encountered (e.g., due to symlink issues), we log an error but continue on, instead of refusing to any work.

[zertosh]

I've had similar problems before, but I ended up going with find ... | xargs jscodeshift since that gives me way more control (e.g. exclude node_modules). Just thinking out loud, I wonder if jscodeshift should be in the business of directory walking at all?

[cpojer]

@zertosh it was added mainly as a convenience. I think jscodeshift should provide a reasonable default.

[zertosh]

Fair enough!

[fkling]

One issue with find and xargs is that if you have too many files, xargs will spawn multiple jscodeshift processes. But I guess we can fix that too by letting jscodeshift read from stdin.