Fixed some Dialyzer issues.

Removed some apps from the build_plt Makefile target to speed up Dialyzer PLT generation.

Change the PLT-related Makefile targets to depend on all. Dialyzer needs the dependencies in place to generate PLTs.

Added <code>{search_index, binary()}</code> to the <code>-spec</code> for <code>server_prop</code>. This property describes a Yokozuna index. This gets rid of the following Dialyzer warning:

<pre>
riakc_pb_socket.erl:919: The call riakc_pb_socket:set_bucket(Pid::any(),Bucket::any(),[{'search_index',_},...]) will never return since the success typing is (pid(),binary(),[{'allow_mult',boolean()} | {'n_val',pos_integer()}]) -> 'ok' | {'error',_} and the contract is (pid(),bucket(),bucket_props()) -> 'ok' | {'error',term()}
</pre>

Fixed a <code>--spec</code> with the parameters in the wrong order causing the following Dialyzer warning:

<pre>
riakc_register.erl:93: Invalid type specification for function riakc_register:set/2. The success typing is (binary(),riakc_register:register()) -> riakc_register:register()
</pre>