Shorten the jasmine async timeout
Add ConnectionPool#begin, Transaction
Add server-side Repository class

On the server, a Repository object holds the following things:
  - a database connection
    (this could be a connection pool or a transaction object)
  - references to tables
  - an identity map (not yet added)

Relations retrieve their repository from their underlying
record class. Right now there is just one Repository,
but later we'll allow them to be cloned. This will allow
for each request to have its own identity map, and for
keeping track of separate database connections during 
transactions.
Move singleton Repository to client