tests: use locate to find files for pyflakes check

Based on a suggestion by Yuya Nishihara

tests/test-check-pyflakes.t

@@ -1,21 +1,21 b''
 #if test-repo pyflakes
 
   $ cd "`dirname "$TESTDIR"`"
 
 run pyflakes on all tracked files ending in .py or without a file ending
 (skipping binary file random-seed)
 
-  $ hg manifest 2>/dev/null | egrep "\.py$|^[^.]*$" | grep -v /random_seed$ \
+  $ hg locate 'set:**.py or grep("^!#.*python")' 2>/dev/null \
   > | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
   contrib/win32/hgwebdir_wsgi.py:*: 'win32traceutil' imported but unused (glob)
   setup.py:*: 'sha' imported but unused (glob)
   setup.py:*: 'zlib' imported but unused (glob)
   setup.py:*: 'bz2' imported but unused (glob)
   setup.py:*: 'py2exe' imported but unused (glob)
   tests/hghave.py:*: '_lsprof' imported but unused (glob)
   tests/hghave.py:*: 'publish_cmdline' imported but unused (glob)
   tests/hghave.py:*: 'pygments' imported but unused (glob)
   tests/hghave.py:*: 'ssl' imported but unused (glob)
   contrib/win32/hgwebdir_wsgi.py:93: 'from isapi.install import *' used; unable to detect undefined names (glob)
   
 #endif