Running the following script provokes causes Blender to
fail with a SIGSEGV:

import Blender.Window

def make_callback(func):
def callback(filename):
print "start callback"
func(filename)
print "end callback"
return callback

def poing(filename):
print "filename =", filename

Blender.Window.FileSelector(make_callback(poing),'Poing')

The problem is caused by
blender/python/api2_2x/Window.c:M_Window_FileSelector()
which fails to Py_INCREF(EXPP_FS_PyCallback) before
returning. If this is added, then the corresponding
Py_DECREF must be done prior to setting
EXPP_FS_PyCallback = NULL, ie in getSelectedFile(), and
also at the top of M_Window_FileSelector(), prior to
calling PyArg_ParseTuple(), to handle the case where
the user canceled the file select hence
getSelectedFile() never got called hence
EXPP_FS_PyCallback is still not NULL.