Delay importing sys.getrefcount until needed

This makes it possibly to at least install on PyPy

Addresses: GH-4 ("pypy compatibility")

Author: msabramo

smmap/mman.py

@@ -10,7 +10,6 @@
 
 from weakref import ref
 import sys
-from sys import getrefcount
 from functools import reduce
 
 __all__ = ["StaticWindowMapManager", "SlidingWindowMapManager", "WindowCursor"]

smmap/util.py

@@ -12,8 +12,6 @@
     from mmap import PAGESIZE as ALLOCATIONGRANULARITY
 #END handle pythons missing quality assurance
 
-from sys import getrefcount
-
 __all__ = [ "align_to_mmap", "is_64_bit",
             "MapWindow", "MapRegion", "MapRegionList", "ALLOCATIONGRANULARITY"]
 
@@ -210,6 +208,7 @@ def includes_ofs(self, ofs):
 
     def client_count(self):
         """:return: number of clients currently using this region"""
+        from sys import getrefcount
         # -1: self on stack, -1 self in this method, -1 self in getrefcount
         return getrefcount(self)-3
 
@@ -256,6 +255,7 @@ def __init__(self, path_or_fd):
 
     def client_count(self):
         """:return: amount of clients which hold a reference to this instance"""
+        from sys import getrefcount
         return getrefcount(self)-3
 
     def path_or_fd(self):