dialyzer: Add support for multiple PLTs

This new feature is able to take multiple PLTs, merge them during the
start of the analysis, and work from there. This works provided that
the PLTs do not have a module with the same name appearing in more
than one PLT.

The PLTs are created in the usual way:

    dialyzer --build_plt --output_plt PLT_1  FILES_TO_INCLUDE
    ...
    dialyzer --build_plt --output_plt PLT_N  FILES_TO_INCLUDE

and then can be used in either of the following ways:

    dialyzer  FILES_TO_ANALYZE  --plts PLT_1 ... PLT_N
or:
    dialyzer --plts PLT_1 ... PLT_N -- FILES_TO_ANALYZE

(Note the -- delimiter in the second case)

1 files changed, 13 insertions, 6 deletions

diff --git a/lib/dialyzer/src/dialyzer_options.erl b/lib/dialyzer/src/dialyzer_options.erl
index 010625b7bd..2c0afa6e2b 100644
--- a/lib/dialyzer/src/dialyzer_options.erl
+++ b/lib/dialyzer/src/dialyzer_options.erl
@@ -53,14 +53,21 @@ build(Opts) ->
   InitPlt = dialyzer_plt:get_default_plt(),
   DefaultOpts = #options{},
   DefaultOpts1 = DefaultOpts#options{legal_warnings = DefaultWarns1,
-				      init_plt = InitPlt},
-  try 
-    NewOpts = build_options(Opts, DefaultOpts1),
+                                     init_plts = [InitPlt]},
+  try
+    Opts1 = preprocess_opts(Opts),
+    NewOpts = build_options(Opts1, DefaultOpts1),
     postprocess_opts(NewOpts)
   catch
     throw:{dialyzer_options_error, Msg} -> {error, Msg}
   end.
 
+preprocess_opts([]) -> [];
+preprocess_opts([{init_plt, File}|Opts]) ->
+  [{plts, [File]}|preprocess_opts(Opts)];
+preprocess_opts([Opt|Opts]) ->
+  [Opt|preprocess_opts(Opts)].
+
 postprocess_opts(Opts = #options{}) ->
   Opts1 = check_output_plt(Opts),
   adapt_get_warnings(Opts1).
@@ -144,9 +151,9 @@ build_options([{OptionName, Value} = Term|Rest], Options) ->
       build_options(Rest, Options#options{from = Value});
     get_warnings ->
       build_options(Rest, Options#options{get_warnings = Value});
-    init_plt ->
-      assert_filenames([Term], [Value]),
-      build_options(Rest, Options#options{init_plt = Value});
+    plts ->
+      assert_filenames(Term, Value),
+      build_options(Rest, Options#options{init_plts = Value});
     include_dirs ->
       assert_filenames(Term, Value),
       OldVal = Options#options.include_dirs,