When an include file is set in a private path (i.e. src/), the rebar3
compiler would not add them to the {i, Path} params -- only include/ and
the project root were being added.
This meant that when some extra source directories were added to the
compile job, such as test/ when running under the test profile, the
private include paths could not be shared with the test module.
This patch fixes the issues (and adds tests) for such a specific case by
adding all the configured include paths to the {i, Path} erl_opts
arguments, yielding successful compile runs.
Fred Hebert