The latest version of erlydtl requires that custom tag modules be in
the path when templates are compiled. Without this change rebar silently
exits when using the custom_tags_modules option.

Automatically include modules with callback attributes in
erl_first_files.

* consolidate options
 * add support for building executables

Before copying the .erl files to the .eunit directory ensure that they
are deleted if they already exist. This prevents EACCES errors to happen
when trying to re-copy .erl files that are read-only.

a) make_symlink throws "not supported" on OS < Vista (e.g. 2003)
b) tarball creation stores windows symlinks as absolute paths
   instead of relative, causing service to fail to start after upgrade
   is made permanent.

Error report killing inet_gethost_native after eunit