_.once has the problem that if you call the once'd function while it is
still in progress (re-entrantly or in another Fiber), it returns
undefined immediately. That's bad for uniload! uniload already has a
cache, so just use that. (In the future, perhaps detect an attempt to
uniload something that's currently in the process of being uniloaded in
another fiber and block until the other fiber is ready.)
Using instanceof with things you've uniloaded is a little sketchy: maybe
two different uniload calls will end up with two different copies of
Package.meteor.Meteor.Error, and it seems kind of hairy to ensure you're
not mixing and matching copies. However, Meteor.Errors are all tagged
with a string errorType, which fills me with much less fear,
uncertainty, and doubt than instanceof.
If you happen to introduce a circular require into the stack, this
object will be undefined.
Instead, hang on to `require('./run-log.js')`, which is the exports
module which does get filled in later.
The rationale: RunLog is an object that is hardcoded around managing two
other singletons: stdout and stderr. Having multiple RunLogs wouldn't
work well without improving RunLog to have the ability to control other
streams.
We'd like to be able to use RunLog from other places in the tool, most
notably from code called from bundler (while running an app) such as the
npm updater. But threading a RunLog object through that code is
difficult (especially as bundling takes a detour through
release.current.library).
