Sample solutions.

* The solutions for p1-1, p1-2, and p2 are good enough.  They
  pass all the appropriate tests in the grading directory.

* The solution for p3 is terrible.  For example, there's no locking at
  all.  I just wrote it to make sure that the project was possible
  given the tools that we gave the students.  It also suffers from bit
  rot and won't actually apply anymore.