nix-store -q --roots: Respect the gc-keep-outputs/gc-keep-derivations settings

So if a path is not garbage solely because it's reachable from a root
due to the gc-keep-outputs or gc-keep-derivations settings, ‘nix-store
-q --roots’ now shows that root.

src/libstore/worker-protocol.hh

@@ -6,7 +6,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION 0x10c
+#define PROTOCOL_VERSION 0x10d
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -42,6 +42,7 @@ typedef enum {
     wopQuerySubstitutablePathInfos = 30,
     wopQueryValidPaths = 31,
     wopQuerySubstitutablePaths = 32,
+    wopQueryValidDerivers = 33,
 } WorkerOp;