add a sample of FLUX code

These samples were taken from the paper "Flux: A Language for
Programming High-Performance Servers", by Burns et al and Flux V0.02
which can be found here:

https://plasma.cs.umass.edu/emery/flux.1.html

samples/FLUX/test.fx

@@ -0,0 +1,38 @@
+// concrete node signatures
+Listen ()
+  => (int socket);
+
+ReadRequest (int socket)
+  => (int socket, bool close, image_tag *request);
+
+CheckCache (int socket, bool close, image_tag *request)
+  => (int socket, bool close, image_tag *request);
+
+// omitted for space:
+// ReadInFromDisk, StoreInCache
+Compress (int socket, bool close, image_tag *request, __u8 *rgb_data)
+  => (int socket, bool close, image_tag *request);
+Write (int socket, bool close, image_tag *request)
+  => (int socket, bool close, image_tag *request);
+Complete (int socket, bool close, image_tag *request) => ();
+
+// source node
+source Listen => Image;
+
+// abstract node
+Image = ReadRequest -> CheckCache -> Handler -> Write -> Complete;
+
+// predicate type & dispatch
+typedef hit TestInCache;
+Handler:[_, _, hit] = ;
+Handler:[_, _, _] =
+ReadInFromDisk -> Compress -> StoreInCache;
+
+// error handler
+handle error ReadInFromDisk => FourOhFor;
+
+// atomicity constraints
+atomic CheckCache:{cache};
+atomic StoreInCache:{cache};
+atomic Complete:{cache};
+