Fix typos, especially those that end up in the Nix manual

src/libstore/local-store.cc

@@ -991,7 +991,7 @@ void LocalStore::setSubstituterEnv()
 {
     if (didSetSubstituterEnv) return;
 
-    /* Pass configuration options (including those overriden with
+    /* Pass configuration options (including those overridden with
        --option) to substituters. */
     setenv("_NIX_OPTIONS", settings.pack().c_str(), 1);
 

src/libstore/local-store.hh

@@ -177,7 +177,7 @@ public:
 
     /* Register the validity of a path, i.e., that `path' exists, that
        the paths referenced by it exists, and in the case of an output
-       path of a derivation, that it has been produced by a succesful
+       path of a derivation, that it has been produced by a successful
        execution of the derivation (or something equivalent).  Also
        register the hash of the file system contents of the path.  The
        hash must be a SHA-256 hash. */