libopenflow: Fix ofp_phy_port _validate()

This is a regression caused by a recent improvement.
libopenflow: Use more symbolic constants

Many things were using hardcoded literals.
libopenflow: Minor cleanup
libopenflow: Better default for port_stats_request

The port was defaulting to 0, but should be OFPP_NONE.
libopenflow: Improve adding of port_stats

port_stats objects can be added as an easy way of summing the counters.
Previously, this lost the port_no value.  Now, it is retained when it
is the same in both the left and right operand.
openflow: Fix docsting for keepalive
openflow: Add --timeout option to keepalive
implement ryu-compatible cbench app
remove unnecessary bash dependency
Merge pull request #59 from yamt/cbench2

implement ryu-compatible cbench app
Merge pull request #58 from yamt/unbash

remove unnecessary bash dependency
cbench: Minor tweaks

Use addListeners() instead of listenTo().
pox/boot: Adjust magic sh invoke thing

Apparently at least the Mac version of sh has an echo which
doesn't have the -n switch, so -n was getting echoed with the
recent pull request in place.

This should fix that.
l3_learning: Fix lost packet expiration

The tuple used to index the lost packet buffer was documented
backwards, and used backwards in one place.  This fixes that.

The outstanding ARP buffer's index tuple was also documented
backwards (though apparently only ever used correctly), and
this fixes that too.

Totally untested.  Bug reported by wyanan@mail.ustc.edu.cn
packet: Halfhearted attempt to fix up DNS packing

I think this actually needs a fair amount of work, but this is a
quick stab which at least sort of fixes some stuff?  Please file
issues with traces that elicit bad behavior.
pxpcap: Add _time property to parser

The _sec and _time properties probably need some tweaking.  Or maybe
their names need to be swapped.  And the datetime one could have usecs
added in, I believe.
pxpcap: Fix wire size / cap size mixup

These were reversed.  Fixed.
pxpcap: Add utilities for writing pcap files
core: Don't log up message if we're already down
pxpcap: Add dump_trace utility component

This is a quick hack of the packet dump app, which just dumps
packets from a pcap file instead of from packet_ins.