Reduce Windows page size to 4KB

As of right now, there is no reliable way to determine the Windows
default page size without including additional modules.  For for
the safest assumption of 4KB.  Linux, until 2.6.38 with transparent
huge pages, uses 4KB by default as well.

slbackup.py

@@ -38,8 +38,9 @@
 try:
     import resource
 except ImportError:
-    # well, must be windows, assume an 8MB slab
-    _DEFAULT_OS_BUFLEN=8*1024*1024
+    # well, must be windows, assume an 4Kb slab
+    # regardless if long mode is supported
+    _DEFAULT_OS_BUFLEN=4*1024
 else:
     _DEFAULT_OS_BUFLEN=resource.getpagesize()