Add ExtractObject usage comment (PLAT-673)
Merge pull request #131 from datacratic/PLAT-673-allow-path-validation-with-extractObject

Added connection and request parameters to extractObject (PLAT-673).
fs_utils: return empty FsObjectInfo for missing local files
Added trailing separators to HTTP chunks (TRIVIAL)
Added response code extractor for client HttpHeader usage (TRIVIAL)
Added onHeader callback to HTTP REST client
Don't accumulate request body when HttpClient onData specified
Removed dead code from RestServiceEndpoint (TRIVIAL)
Removed verbose debugging from connection handler (TRIVIAL)
Handle RestConnectionHandler asynchronous disconnects

When a RestConnectionHandler processes a response asynchronously, it takes a reference to the
connection and then returns.  Sometime later it will asynchronously write to the connection and
then close it.  As soon as it returns, it loses the lock on the connection, and it is possible
for the other end to break the connection and for it to be shutdown.  In that case, the
connection is dangling and we were getting a segfault.

We now handle that by trapping the disconnect and setting a mutex-protected zombie flag.  All
operations that require the connection also take the mutex to avoid a race condition.  If
a response to the connection is attempted, it will notice that the connection is a zombie and
exit immediately.  This doesn't solve the problem of releasing the connection, but does at
least avoid the segfault.
Merge branch 'master' of github.com:datacratic/soa into datacratic-internal-branch-6