Make `make test` run unit tests too

refs https://github.com/neovim/neovim/pull/2124#discussion_r26107174

Unlike Travis, `make test` currently only runs functional tests.
This can cause confusion since one might (understandably) think that `make
test` runs unit tests too, which it doesn't.

The `oldtest` target is still left out because it's quite slow and
Travis already runs it.

Makefile

@@ -89,14 +89,14 @@ functionaltest: | nvim
 testlint: | nvim
 	$(BUILD_CMD) -C build testlint
 
-test: functionaltest
-
 unittest: | nvim
 	+$(BUILD_CMD) -C build unittest
 
 benchmark: | nvim
 	+$(BUILD_CMD) -C build benchmark
 
+test: functionaltest unittest
+
 clean:
 	+test -d build && $(BUILD_CMD) -C build clean || true
 	$(MAKE) -C src/nvim/testdir clean