This adds a new test for readfile. Interestingly, it actually caught a
small bug, which was also fixed with this commit. I think the bug was
actually always masked, because it only occurred on shutdown, and in
this case we often don't care about how the stream exited, but it's a
good example of how a test case focused on just one small aspect can be
important.
As an aside, this test case also would have caught the bug fixed in
94c40909cc and by reverting that patch it
indeed fails.
Readfile had a bug where it sent an empty string on startup. This has
ben fixed, and it now waits until the file contents are ready before
sending a string.
This unbreaks the mcl bindata code. Of course we could change the parser
to allow this prefix, but this is cleaner. The packages still have a
core prefix, which it seems we could also remove, but this isn't
particularly important for anything.
