add comment for global apply_profiles and log message for bad bootstrap lock file

bootstrap

@@ -285,6 +285,7 @@ get_deps() ->
     case file:consult("rebar.lock") of
         {ok, [[]]} ->
             %% Something went wrong in a previous build, lock file shouldn't be empty
+            io:format("Empty list in lock file, deleting rebar.lock~n"),
             ok = file:delete("rebar.lock"),
             {ok, Config} = file:consult("rebar.config"),
             proplists:get_value(deps, Config);

src/rebar_state.erl

@@ -290,6 +290,9 @@ apply_profiles(State, [default]) ->
     State;
 apply_profiles(State=#state_t{default = Defaults, current_profiles=CurrentProfiles}, Profiles) ->
     AppliedProfiles = case Profiles of
+                          %% Head of list global profile is special, only for use by rebar3
+                          %% It does not clash if a user does `rebar3 as global...` but when
+                          %% it is the head we must make sure not to prepend `default`
                           [global | _] ->
                               Profiles;
                           _ ->