Wrap Erlang scripts to provide missing 'sed' and 'awk'.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Elixir: Fix impurity with Erlang.

The bash scripts of elixir contain some references to `erl'. This
patch wraps the scripts and extends PATH so `erl' is available.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Merge pull request #865 from the-kenny/fix-erlang-elixir

Fix purity of Elixir and Erlang