Upgrade to Go 1.4

This change set upgrades Prometheus to use Go 1.4
The other modifications were intended to compare benchmarks between the
old and new versions using `golang.org/x/tools/cmd/benchcmp`.

```
benchmark                                old ns/op      new ns/op     delta
BenchmarkTargetManager-8                 38866          19355         -50.20%
BenchmarkTargetPool-8                    114763         58989         -48.60%
BenchmarkFingerprintLockerParallel-8     747            752           +0.67%
BenchmarkFingerprintLockerSerial-8       39.0           39.1          +0.26%
BenchmarkAppend-8                        2020           2553          +26.39%
BenchmarkFuzz-8                          1185584705     506752314     -57.26%
BenchmarkLabelPairs-8                    753            903           +19.92%

benchmark                                old allocs     new allocs     delta
BenchmarkTargetManager-8                 41             46             +12.20%
BenchmarkTargetPool-8                    682            460            -32.55%
BenchmarkFingerprintLockerParallel-8     0              0              +0.00%
BenchmarkFingerprintLockerSerial-8       0              0              +0.00%
BenchmarkAppend-8                        11             15             +36.36%
BenchmarkFuzz-8                          2269055        1061400        -53.22%
BenchmarkLabelPairs-8                    12             12             +0.00%

benchmark                                old bytes      new bytes     delta
BenchmarkTargetManager-8                 8755           7160          -18.22%
BenchmarkTargetPool-8                    82621          41342         -49.96%
BenchmarkFingerprintLockerParallel-8     0              0             +0.00%
BenchmarkFingerprintLockerSerial-8       0              0             +0.00%
BenchmarkAppend-8                        289            293           +1.38%
BenchmarkFuzz-8                          2307248006     586094916     -74.60%
BenchmarkLabelPairs-8                    316            304           -3.80%
```

.gitignore

@@ -27,6 +27,7 @@ core
 
 *-stamp
 prometheus
+benchmark.txt
 
 .#*
 command-line-arguments.test

Makefile

@@ -49,8 +49,8 @@ tag:
 $(BUILD_PATH)/cache/$(GOPKG):
 	$(CURL) -o $@ -L $(GOURL)/$(GOPKG)
 
-benchmark: test
-	$(GO) test $(GO_TEST_FLAGS) -test.bench='Benchmark' ./...
+benchmark: config dependencies tools
+	$(GO) test $(GO_TEST_FLAGS) -test.run='NONE' -test.bench='.*' -test.benchmem ./... | tee benchmark.txt
 
 clean:
 	$(MAKE) -C $(BUILD_PATH) clean

Makefile.INCLUDE

@@ -26,7 +26,7 @@ MAC_OS_X_VERSION ?= 10.8
 
 BUILD_PATH = $(PWD)/.build
 
-GO_VERSION	 := 1.3.3
+GO_VERSION	 := 1.4
 GOOS		  = $(subst Darwin,darwin,$(subst Linux,linux,$(OS)))
 
 ifeq ($(GOOS),darwin)