Fix handling of logical lines with noqa

When attempting to centralize all inline NoQA handling in the StyleGuide
we inadvertently broke plugins relying on it in combination with checker
state. For example, the check for E402 relies both on NoQA and the state
to determine if it has seen a non-import line. Placing NoQA on the sole
line that is not an import is more elegant than placing it on each of
the following import lines.

Closes #186

src/flake8/processor.py

@@ -2,7 +2,6 @@
 import contextlib
 import io
 import logging
-import re
 import sys
 import tokenize
 
@@ -47,8 +46,6 @@ class FileProcessor(object):
     - :attr:`verbose`
     """
 
-    NOQA_FILE = re.compile(r'\s*# flake8[:=]\s*noqa', re.I)
-
     def __init__(self, filename, options, lines=None):
         """Initialice our file processor.
 
@@ -147,6 +144,7 @@ class FileProcessor(object):
             self.previous_logical = self.logical_line
         self.blank_lines = 0
         self.tokens = []
+        self.noqa = False
 
     def build_logical_line_tokens(self):
         """Build the mapping, comments, and logical line lists."""
@@ -189,9 +187,12 @@ class FileProcessor(object):
     def build_logical_line(self):
         """Build a logical line from the current tokens list."""
         comments, logical, mapping_list = self.build_logical_line_tokens()
+        joined_comments = ''.join(comments)
         self.logical_line = ''.join(logical)
+        if defaults.NOQA_INLINE_REGEXP.search(joined_comments):
+            self.noqa = True
         self.statistics['logical lines'] += 1
-        return ''.join(comments), self.logical_line, mapping_list
+        return joined_comments, self.logical_line, mapping_list
 
     def split_line(self, token):
         """Split a physical line's line based on new-lines.
@@ -316,12 +317,12 @@ class FileProcessor(object):
         """Check if ``# flake8: noqa`` is in the file to be ignored.
 
         :returns:
-            True if a line matches :attr:`FileProcessor.NOQA_FILE`,
+            True if a line matches :attr:`defaults.NOQA_FILE`,
             otherwise False
         :rtype:
             bool
         """
-        ignore_file = self.NOQA_FILE.search
+        ignore_file = defaults.NOQA_FILE.search
         return any(ignore_file(line) for line in self.lines)
 
     def strip_utf_bom(self):