Based on my testing, these seem to prefer not having a backslash on the end.
Merge pull request #299 from greggles/patch-1

Remove backslash from site alias drush-dir docs.
Fix #293. Change argument handling in user commands to use _csv_to_array() helper function.
Remove superfluous command callback specifications in user.drush.inc.
Enable cache while making the core projects in-place.

Contrib projects are made in a subprocess using the `make-process`
backend command, and they get the `'cache'` parameter set properly.
This is not the case of core, which is built separately.

This means that, in particular, any specified core patch will
not be cached.