Convert the E266 fixer to be a more usual one

This still ends up fixing cases of E265 which overlap with E266
but doesn't go out of its way to do so if E265 is disabled. This
ought to be fine since pycodestyle doesn't seem to ever complain
about E266 on any lines affected by E265.

autopep8.py

@@ -831,6 +831,28 @@ def fix_e265(self, result):
 
         self.source[result['line'] - 1] = fixed
 
+    def fix_e266(self, result):
+        """Fix too many block comment hashes."""
+
+        source = ''.join(self.source)
+        # TODO: don't recompute this every time!
+        ignored_line_numbers = multiline_string_lines(
+            source,
+            include_docstrings=True) | set(commented_out_code_lines(source))
+
+        if result['line'] in ignored_line_numbers:
+            return
+
+        # Leave stylistic outlined blocks alone.
+        target = self.source[result['line'] - 1]
+        if target.strip().endswith('#'):
+            return
+
+        indentation = _get_indentation(target)
+        fixed = indentation + '# ' + target.lstrip('# \t')
+
+        self.source[result['line'] - 1] = fixed
+
     def fix_e271(self, result):
         """Fix extraneous whitespace around keywords."""
         line_index = result['line'] - 1
@@ -1696,48 +1718,6 @@ def split_and_strip_non_empty_lines(text):
     return [line.strip() for line in text.splitlines() if line.strip()]
 
 
-def fix_e266(source, aggressive=False):  # pylint: disable=unused-argument
-    """Format block comments."""
-    if '#' not in source:
-        # Optimization.
-        return source
-
-    ignored_line_numbers = multiline_string_lines(
-        source,
-        include_docstrings=True) | set(commented_out_code_lines(source))
-
-    fixed_lines = []
-    sio = io.StringIO(source)
-    for (line_number, line) in enumerate(sio.readlines(), start=1):
-        if (
-            line.lstrip().startswith('#') and
-            line_number not in ignored_line_numbers and
-            not pycodestyle.noqa(line)
-        ):
-            indentation = _get_indentation(line)
-            line = line.lstrip()
-
-            # Normalize beginning if not a shebang.
-            if len(line) > 1:
-                pos = next((index for index, c in enumerate(line)
-                            if c != '#'))
-                if (
-                    # Leave multiple spaces like '#    ' alone.
-                    (line[:pos].count('#') > 1 or line[1].isalnum() or
-                        not line[1].isspace()) and
-                    line[1] not in ':!' and
-                    # Leave stylistic outlined blocks alone.
-                    not line.rstrip().endswith('#')
-                ):
-                    line = '# ' + line.lstrip('# \t')
-
-            fixed_lines.append(indentation + line)
-        else:
-            fixed_lines.append(line)
-
-    return ''.join(fixed_lines)
-
-
 def refactor(source, fixer_names, ignore=None, filename=''):
     """Return refactored code using lib2to3.