wafsamba: create unique names when building shared modules

wafsamba: create unique names when building shared modules

After commit 76fdcf5c15bd904c3686f0c2dd93d27486c61ca4, we could endup
with bin/default/source3/auth/libauth-samba4.so being created two times.
Once by SAMBA3_LIBRARY('auth',...) and once again by SAMBA3_MODULE('auth_samba4', ...).

As a result bin/default/source3/auth/libauth-samba4.so gets randomly
overwritten.

SAMBA3_MODULE('auth_samba4', ...) results in
bin/default/source3/auth/libauth_module_samba4.so now.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10112

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jelmer Vernooij <jelmer@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Mon Jan 19 04:43:53 CET 2015 on sn-devel-104