Unit tests do not compile, because INCLUDE_DIR is incorrect

I just downloaded the latest master code (ad4dfd8) and the unit tests don't compile. I know they aren't finished examples, but I thought you'd like to know the include dir is broken.

The test/unit/test1/makefile should be updated to:

`INCLUDE_DIRS += ../../../src`

Side note: Isn't convention that the file is Makefile? Make doesn't seem to care, so maybe that doesn't matter.