By default, just assume a tty

Use of cgo is a pain for cross-compilation, and also if the person
running the build doesn't have a C compiler installed. So make the
default version of `isatty.Isatty()` just return true. The only effect
of this change is that progress information is output by default.

If you want to really use `isatty()`, compile with

    make USE_ISATTY=t

or

    go build --tags isatty

Users can still control the output of progress information using
`--progress`/`--no-progress`.

Author: mhagger

Makefile

@@ -10,6 +10,10 @@ GOFLAGS := \
 	--tags "static" \
 	-ldflags "-X main.BuildVersion=$(shell git rev-parse HEAD) -X main.BuildDescribe=$(shell git describe --tags --always --dirty)"
 
+ifdef USE_ISATTY
+GOFLAGS := $(GOFLAGS) --tags isatty
+endif
+
 GO_SRCS := $(shell cd $(GOPATH)/src/$(PACKAGE) && $(GO) list -f '{{$$ip := .ImportPath}}{{range .GoFiles}}{{printf ".gopath/src/%s/%s\n" $$ip .}}{{end}}{{range .CgoFiles}}{{printf ".gopath/src/%s/%s\n" $$ip .}}{{end}}{{range .TestGoFiles}}{{printf ".gopath/src/%s/%s\n" $$ip .}}{{end}}{{range .XTestGoFiles}}{{printf ".gopath/src/%s/%s\n" $$ip .}}{{end}}' ./...)
 
 .PHONY: all

isatty/isatty_disabled.go

@@ -0,0 +1,7 @@
+// +build !isatty
+
+package isatty
+
+func Isatty(fd uintptr) (bool, error) {
+	return true, nil
+}

isatty/isatty.go renamed to isatty/isatty_enabled.go

@@ -1,3 +1,5 @@
+// +build isatty
+
 package isatty
 
 /*