Remove errors.wrap helper

`errors.wrap` existed to avoid the conflict between the type,
`errors.cause` and the formal parameter `cause`. The parameter was
renamed to err in #32 so there is no need for the helper.

errors.go

@@ -108,7 +108,16 @@ func Wrap(err error, message string) error {
 	if err == nil {
 		return nil
 	}
-	return wrap(err, message, callers())
+	return struct {
+		cause
+		*stack
+	}{
+		cause{
+			cause:   err,
+			message: message,
+		},
+		callers(),
+	}
 }
 
 // Wrapf returns an error annotating err with the format specifier.
@@ -117,19 +126,15 @@ func Wrapf(err error, format string, args ...interface{}) error {
 	if err == nil {
 		return nil
 	}
-	return wrap(err, fmt.Sprintf(format, args...), callers())
-}
-
-func wrap(err error, msg string, st *stack) error {
 	return struct {
 		cause
 		*stack
 	}{
 		cause{
 			cause:   err,
-			message: msg,
+			message: fmt.Sprintf(format, args...),
 		},
-		st,
+		callers(),
 	}
 }
 
@@ -213,8 +218,6 @@ func location(pc uintptr) (string, int) {
 		return "unknown", 0
 	}
 
-	file, line := fn.FileLine(pc)
-
 	// Here we want to get the source file path relative to the compile time
 	// GOPATH. As of Go 1.6.x there is no direct way to know the compiled
 	// GOPATH at runtime, but we can infer the number of path segments in the
@@ -239,6 +242,7 @@ func location(pc uintptr) (string, int) {
 	// leading separator.
 	const sep = "/"
 	goal := strings.Count(fn.Name(), sep) + 2
+	file, line := fn.FileLine(pc)
 	i := len(file)
 	for n := 0; n < goal; n++ {
 		i = strings.LastIndex(file[:i], sep)
@@ -251,6 +255,5 @@ func location(pc uintptr) (string, int) {
 	}
 	// get back to 0 or trim the leading separator
 	file = file[i+len(sep):]
-
 	return file, line
 }