Add a bit more const, and kill of (finally!) sys_getpwnam and sys_getpwuid.

Add a bit more const, and kill of (finally!) sys_getpwnam and sys_getpwuid.

These might be reimplmented as simple pass-through functions, but all users
really should be doing 'getpwnam_alloc' or 'getpwuid_alloc' to ensure that
there are not shared static buffers.

I don't beleive we actually need a getpw*() cache inside samba - if we do
then I think we should look at our code design first.

(some of these changes are for platforms I don't have access to, but
they look sane)

Andrew Bartlett