Clearing promise contexts after completion

Hello eford, 

Please review the following commits I made in branch 'azulus-callbacks'.

367d49378a58208a81653571ce9e85c080eef44b (2013-04-16 15:43:12 -0700)
Clearing promise contexts

100ca8916bf4c875399c80e674645073d9bf5745 (2013-04-15 15:43:47 -0700)
More doc blocks

6d331555baa2ec53308671273c3f7f005d3c8a57 (2013-04-15 15:42:20 -0700)
+doc blocks

ca8e88efdf4bf7125994eea55757a2d64e672f5d (2013-04-15 15:35:59 -0700)
Removing callbacks in favor of contexts

51bb32161a05ae81ce181dd985d930d94a0c3f7b (2013-04-15 15:21:03 -0700)
Flipped ConnectionPool to use promise contexts

R=eford