[kernel] Let objects inherit caps from superclasses

The main point of this change is to allow "global" capabilities defined
on the base object type. The example here is the clone capability on all
objects, which governs the ability to clone a handle.

Related changes in this commit:
- Renamed `kobject` to `object` as far as the syscall interface is
  concerned. `kobject` is the cname, but j6_cap_kobject_clone feels
  clunky.
- The above change made me realize that the "object <type>" syntax for
  specifying object references was also clunky, so now it's "ref <type>"
- Having to add `.object` on everywhere to access objects in
  interface.exposes or object.super was cumbersome, so those properties
  now return object types directly, instead of ObjectRef.
- syscall_verify.cpp.cog now generates code to check capabilities on
  handles if they're specified in the definition, even when not passing
  an object to the implementation function.

definitions/objects/process.def

@@ -1,9 +1,9 @@
-import "objects/kobject.def"
+import "objects/object.def"
 
 # Processes are a collection of handles and a virtual memory
 # space inside which threads are run.
 
-object process : kobject {
+object process : object {
     uid 0c69ee0b7502ba31
 
     capabilities [
@@ -25,7 +25,7 @@ object process : kobject {
     # Give the given process a handle that points to the same
     # object as the specified handle.
     method give_handle {
-        param target object kobject [handle]           # A handle in the caller process to send
-        param received object kobject [out optional]  # The handle as the recipient will see it
+        param target ref object [handle]          # A handle in the caller process to send
+        param received ref object [out optional]  # The handle as the recipient will see it
     }
 }