Add some test cases for multiline strings.

Since I'm about to add special treatment of multiline strings, I
thought it best to ensure that we preserve the existing behaviour.

Author: gward

testsuite/E50.py

@@ -45,3 +45,11 @@
 ('''
     ''' + ' \
 ')
+#
+#: E501
+'''multiline string
+with a long long long long long long long long long long long long long long long long line
+'''
+#: E501
+'''same thing, but this time without a terminal newline in the string
+long long long long long long long long long long long long long long long long line'''

testsuite/W19.py

@@ -97,6 +97,14 @@ def long_function_name(
 if os.path.exists(os.path.join(path, PEP8_BIN)):
 	cmd = ([os.path.join(path, PEP8_BIN)] +
 	       self._pep8_options(targetfile))
+#: W191
+'''
+	multiline string with tab in it'''
+#: E101 W191
+'''multiline string
+	with tabs
+   and spaces
+'''
 #: E101 W191
 if foo is None and bar is "frop" and \
         blah == 'yeah':

testsuite/W29.py

@@ -6,5 +6,8 @@
 class Foo(object):
 
     bang = 12
+#: W291
+'''multiline
+string with trailing whitespace'''   
 #: W292
 # This line doesn't have a linefeed