GOPATH can have multiple : separated paths in it.

This means that simply adding /bin to the end is not enough. Instead of
setting GOBIN, this version prepends things to the PATH. If GOBIN is
already set, simply prepends GOBIN to PATH.  If not, appends /bin to
each component of GOPATH, then prepends that to PATH.

closes #386

Makefile

@@ -1,30 +1,32 @@
 UNAME := $(shell sh -c 'uname')
 VERSION := $(shell sh -c 'git describe --always --tags')
-ifndef GOBIN
-	GOBIN = $(GOPATH)/bin
+ifdef GOBIN
+PATH := $(GOBIN):$(PATH)
+else
+PATH := $(subst :,/bin:,$(GOPATH))/bin:$(PATH)
 endif
 
 # Standard Telegraf build
 build: prepare
-	$(GOBIN)/godep go build -o telegraf -ldflags \
+	godep go build -o telegraf -ldflags \
 		"-X main.Version=$(VERSION)" \
 		./cmd/telegraf/telegraf.go
 
 # Build with race detector
 dev: prepare
-	$(GOBIN)/godep go build -race -o telegraf -ldflags \
+	godep go build -race -o telegraf -ldflags \
 		"-X main.Version=$(VERSION)" \
 		./cmd/telegraf/telegraf.go
 
 # Build linux 64-bit, 32-bit and arm architectures
 build-linux-bins: prepare
-	GOARCH=amd64 GOOS=linux $(GOBIN)/godep go build -o telegraf_linux_amd64 \
+	GOARCH=amd64 GOOS=linux godep go build -o telegraf_linux_amd64 \
 								-ldflags "-X main.Version=$(VERSION)" \
 								./cmd/telegraf/telegraf.go
-	GOARCH=386 GOOS=linux $(GOBIN)/godep go build -o telegraf_linux_386 \
+	GOARCH=386 GOOS=linux godep go build -o telegraf_linux_386 \
 								-ldflags "-X main.Version=$(VERSION)" \
 								./cmd/telegraf/telegraf.go
-	GOARCH=arm GOOS=linux $(GOBIN)/godep go build -o telegraf_linux_arm \
+	GOARCH=arm GOOS=linux godep go build -o telegraf_linux_arm \
 								-ldflags "-X main.Version=$(VERSION)" \
 								./cmd/telegraf/telegraf.go
 
@@ -86,6 +88,6 @@ test: docker-kill prepare docker-run
 
 # Run "short" unit tests
 test-short: prepare
-	$(GOBIN)/godep go test -short ./...
+	godep go test -short ./...
 
 .PHONY: test