Include formatting check to the make test (and thus also check) rule (#1366)

* Include formatting check to the `make check` rule

... and give it its own standalone target too (make fmt-check)

Show diff on fmt-check failure
Do not allow running "fmt-check" with incompatible go version
Also simplify the `fmt` rule

* Forbid running "make fmt" with Go version != 1.7 or 1.8

* Ignore bindata.go for spelling and formatting checks

also remove duplicated variable assignment for GOFILES

* Run `make fmt`

modules/setting/setting.go

@@ -177,7 +177,7 @@ var (
 
 		// Repository local settings
 		Local struct {
-			LocalCopyPath       string
+			LocalCopyPath string
 		} `ini:"-"`
 	}{
 		AnsiCharset:            "",
@@ -214,7 +214,7 @@ var (
 
 		// Repository local settings
 		Local: struct {
-			LocalCopyPath  string
+			LocalCopyPath string
 		}{
 			LocalCopyPath: "tmp/local-repo",
 		},