[krbdev.mit.edu #7431] Improve documentation for krb5_unparse_name_ext()

[Sumit Bose via RT]

Hi,

the API docs in src/include/krb5/krb5.hin for krb5_unparse_name_ext()
should mention that if name is not NULL it is assumed that it points to
a pre-allocated buffer with a length given by the size parameter. And
that name must be set to NULL if the allocation should be done by the
library.

bye,
Sumit