Fix sketch_source_merger_test.go to use full paths in #line directives

This uses the text/template package to process the sketch file, allowing
it access to the full context. This is a bit overkill, but it is easy
and might be useful for more complex testcases later.

Author: matthijskooijman

Diff for: src/arduino.cc/builder/test/sketch1/merged_sketch.txt

@@ -1,14 +1,14 @@
-#line 1 "sketch.ino"
+#line 1 "{{.sketch.MainFile.Name}}"
 void setup() {
 
 }
 
 void loop() {
 
 }
-#line 1 "old.pde"
+#line 1 "{{(index .sketch.OtherSketchFiles 0).Name}}"
 
-#line 1 "other.ino"
+#line 1 "{{(index .sketch.OtherSketchFiles 1).Name}}"
 String hello() {
   return "world";
 }

Diff for: src/arduino.cc/builder/test/sketch_source_merger_test.go

@@ -34,12 +34,14 @@ import (
 	"arduino.cc/builder/constants"
 	"arduino.cc/builder/types"
 	"github.com/stretchr/testify/require"
-	"io/ioutil"
 	"path/filepath"
 	"strings"
 	"testing"
+	"text/template"
+	"bytes"
 )
 
+
 func TestMergeSketch(t *testing.T) {
 	context := make(map[string]interface{})
 	context[constants.CTX_SKETCH_LOCATION] = filepath.Join("sketch1", "sketch.ino")
@@ -57,9 +59,13 @@ func TestMergeSketch(t *testing.T) {
 
 	source := context[constants.CTX_SOURCE].(string)
 
-	bytes, err1 := ioutil.ReadFile(filepath.Join("sketch1", "merged_sketch.txt"))
+	tpl, err1 := template.ParseFiles(filepath.Join("sketch1", "merged_sketch.txt"))
 	NoError(t, err1)
 
-	expected_source := string(bytes)
+	var buf bytes.Buffer
+	err2 := tpl.Execute(&buf, context)
+	NoError(t, err2)
+
+	expected_source := buf.String()
 	require.Equal(t, expected_source, strings.Replace(source, "\r\n", "\n", -1))
 }