changes in warning message on adding or editing words.

Wording changed and 'cancel' button added.
When the user tries to add or edit words, PCT checks for duplicates and asks the user whether to add/keep as separate entries or add frequency to existing entry. re: issue #791

corpustools/gui/main.py

@@ -359,12 +359,19 @@ def editWord(self, row, word):
                     askBox = QMessageBox()
                     askBox.setWindowTitle("Duplicated words?")
                     askBox.setText(("The word \'{}\' already exists in the corpus. \n"
-                                    "You can keep both as separate entries, \n"
-                                    "or choose to merge the two (i.e., one entry with the added frequency).".format(dialog.word.spelling)))
+                                    "You can keep both as separate entries, or merge the two\n"
+                                    "(i.e., one entry with the added frequency).\n"
+                                    "If there are multiple instances of \'{}\' in the corpus,\n"
+                                    "the frequency will be added to the first such entry"
+                                    .format(dialog.word.spelling, dialog.word.spelling)))
                     askBox.addButton("Keep both as separate entries", QMessageBox.AcceptRole)
                     askBox.addButton("Merge them and add frequency", QMessageBox.RejectRole)
+                    askBox.addButton(QMessageBox.Cancel)
+                    choice = askBox.exec_()
+                    if choice == QMessageBox.Cancel:
+                        return
                     self.corpusModel.removeWord(self.corpusModel.rows[row])
-                    if askBox.exec_() == QMessageBox.AcceptRole:
+                    if choice == QMessageBox.AcceptRole:
                         self.corpusModel.addWord(dialog.word, allow_duplicates=True)
                     else:
                         self.corpusModel.addWord(dialog.word, allow_duplicates=False)
@@ -975,12 +982,18 @@ def createWord(self):
                     askBox = QMessageBox()
                     askBox.setWindowTitle("Duplicated words?")
                     askBox.setText(("Your input \'{}\' already exists in the corpus. \n"
-                                    "You can add it as a separate entry, \n"
-                                    "or simply add frequency to the existing entry.".format(dialog.word.spelling)))
+                                    "You can add it as a separate entry, or simply add frequency to the existing entry.\n"
+                                    "If there are multiple instances of \'{}\' already in the corpus,\n"
+                                    "then frequency will be added to the first such entry."
+                                    .format(dialog.word.spelling, dialog.word.spelling)))
                     askBox.addButton("Add as a separate entry", QMessageBox.AcceptRole)
                     askBox.addButton("Add frequency to the existing word", QMessageBox.RejectRole)
-                    if askBox.exec_() == QMessageBox.AcceptRole:
+                    askBox.addButton(QMessageBox.Cancel)
+                    choice = askBox.exec_()
+                    if choice == QMessageBox.AcceptRole:
                         allow_duplicates = True
+                    elif choice == QMessageBox.Cancel:
+                        return
                 else:
                     allow_duplicates = True
             except KeyError: