Move pointer_equals/2 into the private_builtin module.

library/version_hash_table.m:
library/private_builtin.m:
    Move pointer_equals/2 as above.

    Rename pointer_equals to pointer_equal.

library/private_builtin.m:
    Adjust a comment to say that this module also contains predicates with
    normal definitions.  That is, they're built into the language but not
    built into the compiler.
Rename version_hash_table.equals/2

Rename version_hash_table.equals/2 to equal/2 as this name is more
consistent with the rest of the standard library.  Normally when renaming
predicates and functions in the standard library we deprecate them.
However, version_hash_table.equals/2 hasn't existed for very long and so
very little code depends on it's name.

library/version_hash_table.m:
    As above.