Added get_page_size function.

diff --git a/server/mapping.c b/server/mapping.c
index dc0690c..a273ed5 100644
--- a/server/mapping.c
+++ b/server/mapping.c
@@ -149,6 +149,12 @@
     if (mapping->file) release_object( mapping->file );
 }
 
+int get_page_size(void)
+{
+    if (!page_mask) init_page_size();
+    return page_mask + 1;
+}
+
 /* create a file mapping */
 DECL_HANDLER(create_mapping)
 {