Ensure proper use of include files under different project config scenarios

[oubiwann]

Originally filed here: lfe-rebar3/compile#28

• a project with an lfe include and no additional settings in rebar.confg
• a project with no include but which uses the include from a dep and has no additional settings in rebar.confg
• both of those first two options, but with {lfe_first_files, ["src/.."]}. set in the rebar.confg
• both of those first two options, but with {lfe_opts, [{i,"..."}]}. set in the rebar.confg
• both of those first two options, but with lfe_first_files and lfe_opts set in the rebar.confg

[oubiwann]

I think I've started running into this a fair amount, especially in release builds. We may need to bump this up to the current milestone ...