chgpasswd.c: Added comments to #ifdefs

chgpasswd.c: Added comments to #ifdefs
ipc.c: Caused samba password changing not to be done if UNIX password
       changing requested and not successful.
util.c: Added string_to_sid() and sid_to_string() functions.
lib/rpc/client/cli_samr.c:
lib/rpc/include/rpc_misc.h:
lib/rpc/parse/parse_lsa.c:
lib/rpc/parse/parse_misc.c:
lib/rpc/parse/parse_net.c:
lib/rpc/parse/parse_samr.c:
lib/rpc/server/srv_lsa.c:
lib/rpc/server/srv_lsa_hnd.c:
lib/rpc/server/srv_netlog.c:
lib/rpc/server/srv_samr.c:
lib/rpc/server/srv_util.c: Changes so that instead of passing SIDs
around as char *, they are converted to DOM_SID at the earliest
opportunity, and passed around as that. Also added dynamic memory
allocation of group sids. Preparing to auto-generate machine sid.
Jeremy.