branches: 1.11.2; 1.11.24;
Fix an issue introduced with the prop_stack change: It's not a good idea to
return a 3-value enum from a function declared to return bool. This broke
the recurse case for prop_object_equals(). Instead, declare the object type
equals routine to return a _prop_object_equals_rv_t.

Give the same treatment to the object type free routines: declare them to
return a _prop_object_free_rv_t, and consistently check those return values
againt the enum type.

Tidy up some whitespace while we're here.