OFStateManager: speed up flow expiration

The old expiration timer iterated over all flows, whether or not they even had
timeouts set. Doing this once per second caused problems with slow CPUs and
large flowtables.

The new approach maintains a list of flows sorted by expiration time. Flows
without timeouts are not included in the list. The expiration timer only needs
to iterate over the portion of the list that might have expired.

The worst-case for flow-add in this datastructure is linear. However, if the
controller only uses a single timeout period then we'll always insert at the
end of the list. We walk the list in reverse when inserting so this is constant
time. If this assumption turns out to be invalid then we can replace the linked
list with something fancier.

The expiration code is moved to a new file.
OFStateManager: convert flow expiration to a long running task

The task is started by the periodic timer.
OFStateManager: raise expiration priority
Merge into master from pull request #64:
speed up flow expiration (https://github.com/floodlight/indigo/pull/64)
Merge into master from pull request #65:
update loci to d31b118de44fc5b7e2fc0ad4ebfda04dbf98f9aa (https://github.com/floodlight/indigo/pull/65)
OFStateManager: add listener interfaces

Implemented for packet-in, port status, and controller messages. The goal is to
enable modules to plug in to OFStateManager, receiving controller messages and
reacting to events from the dataplane.
Merge into master from pull request #66:
OFStateManager: add listener interfaces (https://github.com/floodlight/indigo/pull/66)
OFConnectionManager: implement bsn_time_request

See the LOXI input file for details.
Merge into master from pull request #67:
OFConnectionManager: implement bsn_time_request (https://github.com/floodlight/indigo/pull/67)
OFStateManager: fix biglist include
Remove trailing whitespace.
OFConnectionManager: bind listen sockets to specified address

The code was ignoring the configured address and using INADDR_ANY.
Merge into master from pull request #68:
OFConnectionManager: bind listen sockets to specified address (https://github.com/floodlight/indigo/pull/68)
update loci to b8957d6b02d68b19fa531bdfe89783a13d2d4f7f

 * Adds bsn_disable_src_mac_check extension instruction
Merge into master from pull request #69:
update loci to b8957d6b02d68b19fa531bdfe89783a13d2d4f7f (https://github.com/floodlight/indigo/pull/69)
OFConnectionManager: initialize generation ID to 0
Merge into master from pull request #70:
OFConnectionManager: initialize generation ID to 0 (https://github.com/floodlight/indigo/pull/70)
Increase timer event queue length per test team request
Merge into master from pull request #71:
Increase timer event queue length per test team request (https://github.com/floodlight/indigo/pull/71)
Update loci.