Propagate the stdin_display_name to checker and processor

This way plugins like flake8-putty can have access to the correct filename.

src/flake8/processor.py

@@ -55,12 +55,13 @@ class FileProcessor(object):
         :param str filename:
             Name of the file to process
         """
+        self.options = options
         self.filename = filename
         self.lines = lines
         if lines is None:
-            self.lines = self.read_lines()
+            # allow for stdin filename substitution
+            self.filename, self.lines = self.read_lines(filename)
         self.strip_utf_bom()
-        self.options = options
 
         # Defaults for public attributes
         #: Number of preceding blank lines
@@ -268,13 +269,15 @@ class FileProcessor(object):
             self.indent_char = line[0]
         return line
 
-    def read_lines(self):
+    def read_lines(self, filename):
         # type: () -> List[str]
         """Read the lines for this file checker."""
-        if self.filename is None or self.filename == '-':
-            self.filename = 'stdin'
-            return self.read_lines_from_stdin()
-        return self.read_lines_from_filename()
+        if filename is None or filename == '-':
+            filename = self.options.stdin_display_name or 'stdin'
+            lines = self.read_lines_from_stdin()
+        else:
+            lines = self.read_lines_from_filename()
+        return (filename, lines)
 
     def _readlines_py2(self):
         # type: () -> List[str]