Makefile: call Dialyzer with -nn flag

This speeds up 'make dialyzer' for the common case of Erlang/OTP built
without --enable-native-libs.
simplenode.reltool.config: use default sys-level mod_cond setting

As discussed here
http://erlang.org/pipermail/erlang-questions/2012-December/071135.html
change the reltool spec to use the default sys-level mod_cond setting.
Merge pull request #66 from tuncer/dialyzer-no_native

Makefile: call Dialyzer with -nn flag
Merge pull request #43 from tuncer/reltool-mod_cond

simplenode.reltool.config: use default sys-level mod_cond setting
More error logging

rebar throws away some error messages, e.g. the ones generated if the yecc compiler is broken.
Merge pull request #81 from massemanet/patch-1

More error logging