Rename some variables named “recursive” to “method”

This is much less confusing since recursive is no longer a boolean.

src/libstore/binary-cache-store.hh

@@ -79,7 +79,7 @@ public:
         std::shared_ptr<FSAccessor> accessor) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
-        FileIngestionMethod recursive, HashType hashAlgo,
+        FileIngestionMethod method, HashType hashAlgo,
         PathFilter & filter, RepairFlag repair) override;
 
     StorePath addTextToStore(const string & name, const string & s,