Teach the E265 fixer to fix only E265

Previously it would end up changing E266 as well, which the user
may not want it to do (for example if they've disabled E266).

This also adds a battery of tests to excercise the differences
between these errors.

autopep8.py

@@ -825,9 +825,12 @@ def fix_e265(self, result):
         target = self.source[result['line'] - 1]
 
         indent = _get_indentation(target)
-        comment = target.lstrip(' \t#')
+        line = target.lstrip(' \t')
+        pos = next((index for index, c in enumerate(line) if c != '#'))
+        hashes = line[:pos]
+        comment = line[pos:].lstrip(' \t')
 
-        fixed = indent + ('# ' + comment if comment.strip() else '\n')
+        fixed = indent + hashes + (' ' + comment if comment.strip() else '\n')
 
         self.source[result['line'] - 1] = fixed
 

test/test_autopep8.py

@@ -2232,12 +2232,36 @@ def test_e265(self):
         with autopep8_context(line) as result:
             self.assertEqual(fixed, result)
 
+    def test_e265_only(self):
+        line = "##A comment\n#B comment\n123\n"
+        fixed = "## A comment\n# B comment\n123\n"
+        with autopep8_context(line, options=['--select=E265']) as result:
+            self.assertEqual(fixed, result)
+
+    def test_ignore_e265(self):
+        line = "## A comment\n#B comment\n123\n"
+        fixed = "# A comment\n#B comment\n123\n"
+        with autopep8_context(line, options=['--ignore=E265']) as result:
+            self.assertEqual(fixed, result)
+
     def test_e266(self):
         line = "## comment\n123\n"
         fixed = "# comment\n123\n"
         with autopep8_context(line) as result:
             self.assertEqual(fixed, result)
 
+    def test_e266_only(self):
+        line = "## A comment\n#B comment\n123\n"
+        fixed = "# A comment\n#B comment\n123\n"
+        with autopep8_context(line, options=['--select=E266']) as result:
+            self.assertEqual(fixed, result)
+
+    def test_ignore_e266(self):
+        line = "##A comment\n#B comment\n123\n"
+        fixed = "## A comment\n# B comment\n123\n"
+        with autopep8_context(line, options=['--ignore=E266']) as result:
+            self.assertEqual(fixed, result)
+
     def test_e271(self):
         line = 'True and  False\n'
         fixed = 'True and False\n'