Merge pull request #207 from ret2libc/master

driver/main.c: use goto for clean up on errors
bugfix: don't try to parse optional chisel parameters that are not specified
sendmsg and recvmsg don't modify the state and shoud always go through the engine
zsh completion: FILTER-ONLY fields excluded from -p strings
Merge pull request #209 from dkogan/master

zsh completion: FILTER-ONLY fields excluded from -p strings
userspace/sysdig: always notify the formatter of the end of file
userspace/sysdig: flush cout to print the event

When the format is JSON, last event received is not printed until
another event is processed or sysdig terminates.