go/printer, gofmt: use blank to separate import rename from import path

Note that declarations.golden is not using spaces for alignment (so
that the alignment tabs are visible) which is why this change affects
the test cases significantly. gofmt uses spaces for alignment (by default)
and only tabs for indentation.

gofmt -w src misc (no changes)

Fixes #1673.

R=iant
CC=golang-dev
https://golang.org/cl/4388044

src/pkg/go/printer/nodes.go

@@ -1200,7 +1200,7 @@ func (p *printer) spec(spec ast.Spec, n int, doIndent bool, multiLine *bool) {
 		p.setComment(s.Doc)
 		if s.Name != nil {
 			p.expr(s.Name, multiLine)
-			p.print(vtab)
+			p.print(blank)
 		}
 		p.expr(s.Path, multiLine)
 		p.setComment(s.Comment)

src/pkg/go/printer/testdata/declarations.golden

@@ -81,6 +81,35 @@ import (
 	"testing"
 )
 
+// more import examples
+import (
+	"xxx"
+	"much longer name"	// comment
+	"short name"		// comment
+)
+
+import (
+	_ "xxx"
+	"much longer name"	// comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path"	// a comment
+)
+
+import (
+	"package_a"	// comment
+	"package_b"
+	my_better_c "package_c"	// comment
+	"package_d"		// comment
+	my_e "package_e"	// comment
+
+	"package_a"	// comment
+	"package_bb"
+	"package_ccc"	// comment
+	"package_dddd"	// comment
+)
 
 // at least one empty line between declarations of different kind
 import _ "io"

src/pkg/go/printer/testdata/declarations.input

@@ -81,6 +81,35 @@ import (
 	"testing"
 )
 
+// more import examples
+import (
+	"xxx"
+	"much longer name" // comment
+	"short name" // comment
+)
+
+import (
+	_ "xxx"
+	"much longer name" // comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path" // a comment
+)
+
+import (
+	"package_a" // comment
+	"package_b"
+	my_better_c "package_c" // comment
+	"package_d" // comment
+	my_e "package_e" // comment
+
+	"package_a"    // comment
+	"package_bb"
+	"package_ccc"  // comment
+	"package_dddd" // comment
+)
 
 // at least one empty line between declarations of different kind
 import _ "io"