Rebar currently doesn't give any feedback on an invalid command. This change
makes rebar keep track of how many operations each command triggers, if a
particular command doesn't change the count, there were no modules implementing
it. If at the end of handling all commands, tje count is 0, none of the supplied
commands were valid and ?FAIL is called to trigger a non zero exit status.

Erroneously put rebar_pre_script at the end of the app_dir modules
list in the previous commit.

--HG--
extra : rebase_source : b8eaa05914

Uses code:which or cover:is_compiled to get path the beam for chunks

--HG--
extra : rebase_source : 2f2b819e20

missing from the PIPE_DIR definition above, the application won't start and
doesn't log any thing to the expected locations.

Replace rebar_util:get_cwd/0 by rebar_utils:get_cwd/0.  Luckily the
misspelt module name doesn't seem to have caused any harm, since
rebar_app_utils:is_app_dir/0 and rebar_rel_utils:is_rel_dir/0 aren't
called (only their /1 counterparts).

Change from lists:is_member/2 to lists:member/2, since the former
doesn't exist (the bug only affects rebar_plugins).

--HG--
extra : rebase_source : f042bd65d6

--HG--
extra : rebase_source : 5035f025b5

--HG--
extra : rebase_source : cd143fdf55