make test now runs expensive tests.

We use make test as the measure of correctness.
This laxity has let bugs creep into several systems.
This commit changes our target to always run expensive
tests, unless one specifically runs `make test_short`

(we would do well to remove most if not all timing--
that's usually what makes tests take a long time.)

Makefile

@@ -13,20 +13,25 @@ vendor: godep
 install:
 	cd cmd/ipfs && go install
 
-test: test_go test_sharness
+##############################################################
+# tests targets
+
+test: test_expensive
+
+test_short: test_go_short test_sharness_short
 
 test_expensive: test_go_expensive test_sharness_expensive
 
 test_docker:
 	cd dockertest/ && make
 
-test_go:
+test_go_short:
 	go test -test.short ./...
 
 test_go_expensive:
 	go test ./...
 
-test_sharness:
+test_sharness_short:
 	cd test/ && make
 
 test_sharness_expensive: