Update rebar.config

* Added rebar erlydtl_opts to enable debug_info compile option
  for the ErlyDTL .dtl templates
  See <https://github.com/rebar/rebar/issues/49#issuecomment-13310351>
  by @kellymclaughlin
Updated rebar

* Updated rebar binary copied from `deps/meck/rebar` with the `rebar -V` output:

      rebar 2.1.0-pre R14B04 20121230_172201 git 2.1.0-pre-46-g78fa8fc-dirty

* This update includes the change listed in the rebar source tree as follows,
  which solves the `make build_plt/check_plt/dialyzer` glitches due to
  protobuffs `.proto` file compilation without `debug_info` option:

        commit e7be6874d7dded06659a055d497247aba1c90b4c
        Author: Ryan Zezeski <rzezeski@gmail.com>
        Date:   Sun Sep 2 22:30:58 2012 -0400

            Pass compile flags to protobuffs

            By default protobuffs doesn't create beams with debug info.  This
            causes issues when running dialyzer which requires debug info.  Read
            the `erl_opts` config and pass it down to protobuffs compiler.

* FYI, the old `rebar -V` output was:

      rebar 2.0.0 R14B03 20120816_132849 git 1c98f6c
Merge branch 'add-rebar-erlydtl-opts' into add-new-rebar-binary-and-erlydtl-opts
Merge pull request #272 from jj1bdx/add-new-rebar-binary-and-erlydtl-opts

Add new rebar binary and erlydtl opts info toplevel rebar.config for solving dialyzer glitches