Change all realloc() statements to Realloc() (ecxept for tdb.c)

Change all realloc() statements to Realloc() (ecxept for tdb.c)
changed some code to exploit the fact that Realloc(NULL, size) == malloc(size)
fixed some possible mem leaks, or seg faults.

thanks to andreas moroder (mallocs not checked in client/client.c, client/smbumount.c)
(This used to be commit 7f33c01688b825ab2fa9bbb2730bff4f2fa352be)