added a basic dcerpc endpoint mapper to Samba4. Currently only

added a basic dcerpc endpoint mapper to Samba4. Currently only
implements the epm_Lookup() call, I'll add the other important calls
soon. I was rather pleased to find that epm_Lookup() worked first
time, which is particularly surprising given its complexity.

This required quite a bit of new infrastructure:

  * a generic way of handling dcerpc policy handles in the rpc server

  * added type checked varients of talloc. These are much less error
    prone. I'd like to move to using these for nearly all uses of
    talloc.

  * added more dcerpc fault handling code, and translation from
    NTSTATUS to a dcerpc fault code

  * added data_blob_talloc_zero() for allocating an initially zero
    blob

  * added a endpoint enumeration hook in the dcerpc endpoint server
    operations
(This used to be commit 3f85f9b782dc17417baf1ca557fcae22f5b6a83a)