Improve comment about rebuild permissions button in node_configure()

A minor point, but for clarity I suggest changing:

function node_configure() {
  // Only show rebuild button if there is 0 or more than 2 rows in node_access table,
  // or if there are modules that implement node_grant.
...

to

function node_configure() {
  // Only show rebuild button if there are 0 or 2 or more rows in {node_access}
  // table, or if there are modules that implement hook_node_grants().
...

Patch to follow.