Fail lint when FIXMEs are left behind

We typically use TODOs to track future work. While we're hacking,
though, it's helpful to cut some corners (error messages, comments, test
handling, etc). Now, we can mark those bits of code with a FIXME and be
sure that they won't be committed until they're fixed.

Makefile

@@ -101,6 +101,8 @@ lint:
 	-go tool vet $(PKGS) 2>&1 | tee -a lint.log
 	@echo "Checking gofmt"
 	-[ $(GO_VERSION) != "go1.5" ] || gofmt -d . | tee -a lint.log
+	@echo "Checking for unresolved FIXMEs"
+	-git grep -i fixme | grep -v -e Godeps -e vendor -e Makefile | tee -a lint.log
 	@[ ! -s lint.log ]
 
 thrift_example: thrift_gen