MEMORY keytab does not copy keytab_entry keyblock contents

MEMORY keytab does not copy keytab_entry keyblock contents

In krb5_kt_add_entry: The MEMORY keytab does not make a copy of the
keytab_entry keyblock contents - but instead retains a pointer to the
incomming one.

In krb5_kt_get_entry and krb5_kt_get_next - a pointer to internal
keyblock contents memory is returned to the caller - which is subsequently
freed when tht caller invokes krb5_free_keytab_entry_contents.

Solution is to use krb5_copy_keyblock_contents() instead of simply copying
the structure.

Ticket: new

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@19140 dc483132-0cff-0310-8789-dd5450dbe970