R15 support, replace unsetenv with putenv empty string

bootstrap

@@ -25,7 +25,7 @@ main(_Args) ->
     os:putenv("REBAR_PROFILE", "bootstrap"),
     {ok, State} = rebar3:run(["compile"]),
     reset_env(),
-    os:unsetenv("REBAR_PROFILE"),
+    os:putenv("REBAR_PROFILE", ""),
     %% Build erlydtl files (a hook on compile in the default profile) and escript file
     DepsPaths = rebar_state:code_paths(State, all_deps),
     code:add_pathsa(DepsPaths),

src/rebar3.erl

@@ -115,6 +115,8 @@ run_aux(State, RawArgs) ->
     State2 = case os:getenv("REBAR_PROFILE") of
                  false ->
                      State;
+                 "" ->
+                     State;
                  Profile ->
                      rebar_state:apply_profiles(State, [list_to_atom(Profile)])
              end,

test/rebar_profiles_SUITE.erl

@@ -121,7 +121,7 @@ all_deps_code_paths(Config) ->
                                    ["compile"], {ok, [{app, Name}
                                                      ,{dep, "a", "1.0.0"}
                                                      ,{dep, "b", "2.0.0"}]}),
-    os:unsetenv("REBAR_PROFILE"),
+    os:putenv("REBAR_PROFILE", ""),
 
     Paths = rebar_state:code_paths(State, all_deps),
     Path = lists:reverse(["_build", "all_deps_test", "lib", "b", "ebin"]),