Add new API virDomainMemoryStats to header and drivers

Set up the types for the domainMemoryStats function and insert it into the
virDriver structure definition.  Because of static initializers, update
every driver and set the new field to NULL.

* include/libvirt/libvirt.h.in: new API
* src/driver.h src/*/*_driver.c src/vbox/vbox_tmpl.c: add the new
  entry to the driver structure
* python/generator.py: fix compiler errors, the actual python binding is
  implemented later

python/generator.py

@@ -160,7 +160,8 @@ def enum(type, name, value):
 
 functions_failed = []
 functions_skipped = [
-    "virConnectListDomains"
+    "virConnectListDomains",
+    "virDomainMemoryStats"
 ]
 
 skipped_modules = {
@@ -170,6 +171,7 @@ skipped_types = {
 #    'int *': "usually a return type",
      'virConnectDomainEventCallback': "No function types in python",
      'virEventAddHandleFunc': "No function types in python",
+     'virDomainMemoryStatPtr': "Not implemented yet",
 }
 
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