Don't use wildcards to look for .go files in tests makefile

GNU Make's wildcard function does not recurse into subdirectories when
passed the '**' glob, which results in adding a dependency only to .go
files in the first level of subdirectories under the source root.

We shell out to 'find' instead, which catches all .go files in the
given directory.

test/Makefile

@@ -18,19 +18,21 @@ clean:
 
 bins: $(BINS)
 
-bin/random: $(RANDOM_SRC)/**/*.go IPFS-BUILD-OPTIONS
+find_go_files = $(shell find $(1) -name "*.go")
+
+bin/random: $(call find_go_files, $(RANDOM_SRC)) IPFS-BUILD-OPTIONS
 	@echo "*** installing $@ ***"
 	go build $(GOFLAGS) -o bin/random $(RANDOM_SRC)/random
 
-bin/multihash: $(MULTIHASH_SRC)/**/*.go IPFS-BUILD-OPTIONS
+bin/multihash: $(call find_go_files, $(MULTIHASH_SRC)) IPFS-BUILD-OPTIONS
 	@echo "*** installing $@ ***"
 	go build $(GOFLAGS) -o bin/multihash $(MULTIHASH_SRC)/multihash
 
-bin/ipfs: $(IPFS_ROOT)/**/*.go IPFS-BUILD-OPTIONS
+bin/ipfs: $(call find_go_files, $(IPFS_ROOT)) IPFS-BUILD-OPTIONS
 	@echo "*** installing $@ ***"
 	go build $(GOFLAGS) -o bin/ipfs $(IPFS_CMD)
 
-bin/pollEndpoint: $(POLLENDPOINT_SRC)/*.go IPFS-BUILD-OPTIONS
+bin/pollEndpoint: $(call find_go_files, $(POLLENDPOINT_SRC)) IPFS-BUILD-OPTIONS
 	@echo "*** installing $@ ***"
 	go build $(GOFLAGS) -o bin/pollEndpoint $(POLLENDPOINT_SRC)