Add strings needed by Brackets for mozilla/brackets#847

Author: humphd

locales/en-US/editor.properties

@@ -26,6 +26,7 @@ ERROR_PROJECT_SIZE_EXCEEDED=The total size of the files in your project has exce
 
 # File Open/Save Error strings
 
+FILE_EXISTS_HEADER=The file already exists.
 # The {0} here will be replaced by an actual error message
 OPEN_DIALOG_ERROR=An error occurred when showing the open file dialog. (error {0})
 # {0} will be replaced with a filename and {1} will be replaced by an error message
@@ -101,6 +102,10 @@ SAVE_AND_OVERWRITE=Overwrite
 DELETE=Delete
 BUTTON_YES=Yes
 BUTTON_NO=No
+# "Use Imported" as in "Use the new imported version of this file vs. the existing one"
+USE_IMPORTED=Use New File
+# "Keep Existing" as in "Keep the existing version of this file vs. the imported one"
+KEEP_EXISTING=Keep Existing File
 
 # Quick Edit
 
@@ -143,6 +148,7 @@ DND_SUCCESS_UNTAR_TITLE=Untar Completed Successfully
 DND_SUCCESS_UNZIP=Successfully unzipped <b>{0}</b>.
 # {0} will be replaced by a tar filename
 DND_SUCCESS_UNTAR=Successfully untarred <b>{0}</b>.
+DND_FILE_REPLACE=A file named <span class='dialog-filename'>{0}</span> already exists. Do you want to use the new file or keep the existing one?
 
 # Image Viewer
 IMAGE_FILE_TITLE=Image File