Add TextEditor::withGroupingInterval

This method temporarily instructs the editor to apply undo grouping with
a given interval. This way, undo grouping can be made optional without
adding optional arguments to every buffer manipulation method.

src/text-editor.coffee

@@ -68,6 +68,7 @@ class TextEditor extends Model
   suppressSelectionMerging: false
   updateBatchDepth: 0
   selectionFlashDuration: 500
+  groupingInterval: 0
 
   @delegatesMethods 'suggestedIndentForBufferRow', 'autoIndentBufferRow', 'autoIndentBufferRows',
     'autoDecreaseIndentForBufferRow', 'toggleLineCommentForBufferRow', 'toggleLineCommentsForBufferRows',
@@ -1097,7 +1098,7 @@ class TextEditor extends Model
   # execution and revert any changes performed up to the abortion.
   #
   # * `fn` A {Function} to call inside the transaction.
-  transact: (fn) -> @buffer.transact(fn)
+  transact: (fn) -> @buffer.transact(fn, @groupingInterval)
 
   # Extended: Start an open-ended transaction.
   #
@@ -1105,7 +1106,7 @@ class TextEditor extends Model
   # transaction. If you nest calls to transactions, only the outermost
   # transaction is considered. You must match every begin with a matching
   # commit, but a single call to abort will cancel all nested transactions.
-  beginTransaction: -> @buffer.beginTransaction()
+  beginTransaction: -> @buffer.beginTransaction(@groupingInterval)
 
   # Extended: Commit an open-ended transaction started with {::beginTransaction}
   # and push it to the undo stack.
@@ -1117,6 +1118,19 @@ class TextEditor extends Model
   # within the transaction.
   abortTransaction: -> @buffer.abortTransaction()
 
+  # Extended: Set the time interval  over which undo/redo operations are grouped.
+  #
+  # * `interval` A {Number} of milliseconds within which operations should be
+  #   grouped with respec to undo/redo
+  # * `fn` A {Function} to call with the given interval setting
+  withGroupingInterval: (interval, fn) ->
+    previousInterval = @groupingInterval
+    @groupingInterval = interval
+    try
+      fn()
+    finally
+      @groupingInterval = previousInterval
+
   ###
   Section: TextEditor Coordinates
   ###