Permit caller to "prime" PropEr's typeserver and random generator prior to testing

The motivation of this change request is to permit testing of a
module's exported functions by using both PropEr *and* Meck.  Before
Meck is enabled to mock a module, the cache of PropEr's typeserver
must be first populated.  Otherwise, PropEr is unable to gather a
module's specs.

Sample code to illustrate this technique:

````
-spec check_specs(module()) -> term().
check_specs(Mod) ->
    %% pass through to the original Function Under Test (FUT)
    check_specs(Mod, fun(_Module, _Fun, Args) -> meck:passthrough(Args) end, [], []).

-spec check_specs(module(), fun((module(), atom(), list()) -> term())) -> term().
check_specs(Mod, FUT) ->
    check_specs(Mod, FUT, [], []).

-spec check_specs(module(), fun((module(), atom(), list()) -> term()), proplist()) -> term().
check_specs(Mod, FUT, PropErOptions) ->
    check_specs(Mod, FUT, PropErOptions, []).

-spec check_specs(module(), fun((module(), atom(), list()) -> term()), proplist(), proplist()) -> term().
check_specs(Mod, FUT, PropErOptions, MeckOptions) ->
    proper:global_state_erase(),
    proper:global_state_init_size(1),
    case proper_typeserver:get_exp_specced(Mod) of
        {ok, MFAs} ->
            meck:new(Mod, MeckOptions),
            try
                %% @NOTE Expand MFA clauses for larger arity as needed
                Fun = fun({M,F,0}) ->
                              meck:expect(M,F, fun() -> FUT(M, F, []) end);
                         ({M,F,1}) ->
                              meck:expect(M,F, fun(A1) -> FUT(M, F, [A1]) end);
                         ({M,F,2}) ->
                              meck:expect(M,F, fun(A1, A2) -> FUT(M, F, [A1, A2]) end)
                      end,
                lists:foreach(Fun, MFAs),
                proper:check_specs(Mod, PropErOptions)
            after
                meck:unload(Mod)
            end;
        {error,Reason} ->
            error(Reason, [Mod, PropErOptions, MeckOptions])
    end.
````