undefine: Define the new API

This introduces a new API virDomainUndefineFlags to control the
domain undefine process, as the existing API virDomainUndefine
doesn't support flags.

Currently only flag VIR_DOMAIN_UNDEFINE_MANAGED_SAVE is supported.
If the domain has a managed save image, including
VIR_DOMAIN_UNDEFINE_MANAGED_SAVE in @flags will also remove that
file, and omitting the flag will cause undefine process to fail.

This patch also changes the behavior of virDomainUndefine, if the
domain has a managed save image, the undefine will be refused.

include/libvirt/libvirt.h.in

@@ -1200,6 +1200,16 @@ int                     virDomainMemoryPeek (virDomainPtr dom,
 virDomainPtr            virDomainDefineXML      (virConnectPtr conn,
                                                  const char *xml);
 int                     virDomainUndefine       (virDomainPtr domain);
+
+typedef enum {
+    VIR_DOMAIN_UNDEFINE_MANAGED_SAVE = (1 << 0),
+
+    /* Future undefine control flags should come here. */
+} virDomainUndefineFlagsValues;
+
+
+int                     virDomainUndefineFlags   (virDomainPtr domain,
+                                                  unsigned int flags);
 int                     virConnectNumOfDefinedDomains  (virConnectPtr conn);
 int                     virConnectListDefinedDomains (virConnectPtr conn,
                                                  char **const names,