Add indentBasis metadata to pasteboard when copying text

This allows indent to be normalized properly even if the leading whitespace isn't copied from the first line.

src/app/edit-session.coffee

@@ -202,7 +202,8 @@ class EditSession
       maintainPasteboard = true
 
   pasteText: ->
-    @insertText(pasteboard.read()[0], normalizeIndent: true)
+    [text, metadata] = pasteboard.read()
+    @insertText(text, _.extend(metadata ? {}, normalizeIndent: true))
 
   undo: ->
     @buffer.undo(this)

src/app/selection.coffee

@@ -269,8 +269,13 @@ class Selection
   copy: (maintainPasteboard=false) ->
     return if @isEmpty()
     text = @editSession.buffer.getTextInRange(@getBufferRange())
-    text = pasteboard.read()[0] + "\n" + text if maintainPasteboard
-    pasteboard.write(text)
+    if maintainPasteboard
+      [currentText, metadata] = pasteboard.read()
+      text = currentText + '\n' + text
+    else
+      metadata = { indentBasis: @editSession.indentationForBufferRow(@getBufferRange().start.row) }
+
+    pasteboard.write(text, metadata)
 
   fold: ->
     range = @getBufferRange()