Clean up error logs.

Use %v for errors, tidy some messages, make error messages start lowe-case
(as per go guidelines).  Just accumulated nits.

pkg/ui/datafile.go

@@ -27,7 +27,7 @@ import (
 func bindata_read(data []byte, name string) ([]byte, error) {
 	gz, err := gzip.NewReader(bytes.NewBuffer(data))
 	if err != nil {
-		return nil, fmt.Errorf("Read %q: %v", name, err)
+		return nil, fmt.Errorf("read %q: %v", name, err)
 	}
 
 	var buf bytes.Buffer
@@ -35,7 +35,7 @@ func bindata_read(data []byte, name string) ([]byte, error) {
 	gz.Close()
 
 	if err != nil {
-		return nil, fmt.Errorf("Read %q: %v", name, err)
+		return nil, fmt.Errorf("read %q: %v", name, err)
 	}
 
 	return buf.Bytes(), nil
@@ -2694,7 +2694,7 @@ func Asset(name string) ([]byte, error) {
 	if f, ok := _bindata[cannonicalName]; ok {
 		return f()
 	}
-	return nil, fmt.Errorf("Asset %s not found", name)
+	return nil, fmt.Errorf("asset %s not found", name)
 }
 
 // AssetNames returns the names of the assets.
@@ -2739,12 +2739,12 @@ func AssetDir(name string) ([]string, error) {
 		for _, p := range pathList {
 			node = node.Children[p]
 			if node == nil {
-				return nil, fmt.Errorf("Asset %s not found", name)
+				return nil, fmt.Errorf("asset %s not found", name)
 			}
 		}
 	}
 	if node.Func != nil {
-		return nil, fmt.Errorf("Asset %s not found", name)
+		return nil, fmt.Errorf("asset %s not found", name)
 	}
 	rv := make([]string, 0, len(node.Children))
 	for name := range node.Children {