filterpyflakes: allow reexporting pure symbols from cffi modules

cffi modules will do 'from ..pure.<module> import *'.

tests/filterpyflakes.py

@@ -13,6 +13,9 b' for line in sys.stdin:'
     pats = [
         r"undefined name 'WindowsError'",
         r"redefinition of unused '[^']+' from line",
+        # for cffi, allow re-exports from pure.*
+        r"cffi/[^:]*:.*\bimport \*' used",
+        r"cffi/[^:]*:.*\*' imported but unused",
     ]
 
     keep = True

tests/test-check-pyflakes.t

@@ -10,5 +10,5 b' run pyflakes on all tracked files ending'
   > -X mercurial/pycompat.py -X contrib/python-zstandard \
   > 2>/dev/null \
   > | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
-  tests/filterpyflakes.py:38: undefined name 'undefinedname'
+  tests/filterpyflakes.py:41: undefined name 'undefinedname'