erlc: fix two regressions

* headers referenced via -include_lib() were not properly
  resolved to absolute filenames

* .erl files found in sub dirs of src_dirs were not properly
  resolved to absolute filenames
erlc: fix file:open/2 and file:close/1 TODOs

{ok, Fd} = file:open(Source, [read]) and file:close(Fd) must
succeed, or else the subsequent compile:file(Source, Opts) call
would also fail.