fix(leaks): attempt to plug the leaks & filter dead regions

Possible fixing gitpython-developers#31 double mmap increment, stop decrement on
destruction, rely on with... resources.

smmap/mman.py

@@ -43,9 +43,6 @@ def __init__(self, manager=None, regions=None):
         self._ofs = 0
         self._size = 0
 
-    def __del__(self):
-        self._destroy()
-
     def __enter__(self):
         return self
 
@@ -133,8 +130,6 @@ def use_region(self, offset=0, size=0, flags=0):
 
         if need_region:
             self._region = man._obtain_region(self._rlist, offset, size, flags, False)
-            self._region.increment_client_count()
-        # END need region handling
 
         self._ofs = offset - self._region._b
         self._size = min(size, self._region.ofs_end() - offset)
@@ -401,7 +396,7 @@ def make_cursor(self, path_or_fd):
         **Note:** Using file descriptors directly is faster once new windows are mapped as it
         prevents the file to be opened again just for the purpose of mapping it."""
         regions = self._fdict.get(path_or_fd)
-        if regions is None:
+        if not regions or not regions.filter_closed():
             regions = self.MapRegionListCls(path_or_fd)
             self._fdict[path_or_fd] = regions
         # END obtain region for path

smmap/util.py

@@ -273,4 +273,10 @@ def file_size(self):
         # END update file size
         return self._file_size
 
+    def filter_closed(self):
+        for r in list(self):
+            if r._mf.closed:
+                self.remove(r)
+        return self
+
 #} END utility classes