option to force rebuild, default to false

No longer will shadow remove its build cache by default before building. This will speed up rebuilds when only a small number of files change. Occasionally the new -f or --force option may be required to update the problematically stale build cache.

closes #129
configurable buffer sizes

use the following command line options to configure buffers globally for all nodes for which there is no local configuration in the xml file:
 --interface-buffer=N   // network interface receive buffer in bytes
 --socket-recv-buffer=N // socket receive buffer initial size in bytes
 --socket-send-buffer=N // socket send buffer initial size in bytes

Note that the socket buffer values represent an initial size for TCP connections. TCP auto-tuning will further adjust the sizes based on both peers in the connection.

Similarly, each of these options can be configured on a per-node basis by specifying these configs as node attributes in the hosts.xml or similar file:
 <node interfacebuffer="1024000" socketrecvbuffer="256000" socketsendbuffer="128000" ... >

Note that these values will be optional for node elements.

refs #132
Merge branch 'release-patched' into utp
Copy echo plugin to linkprofiler
Rename echo to linkprofiler, and remove files not needed
Make linkprofiler compile (still just does UDP echo)
Rename to linkprofiler and add a test topology
Reduce packet loss so it is likely echo will get through
Log client events
Throw away data read by server
Call clientWritable even if client is done
Send 10 data items, waiting 1 second between them
Disable epoll when sleeping