s4/messaging: Fix undefined reference in linking libMESSAGING-samba4.so

s4/messaging: Fix undefined reference in linking libMESSAGING-samba4.so

Early check for DEVELOPER or ENABLE_SELFTEST configure options inside
messaging_handlers.c leaves us with the following undefined reference
linkage error:

[1315/3712] Linking bin/default/source4/lib/messaging/libMESSAGING-samba4.so
/usr/bin/ld: source4/lib/messaging/messaging.c.4.o: in function
						`imessaging_init_internal':
/root/samba.git/bin/default/../../source4/lib/messaging/messaging.c:472:
		undefined reference to `imessaging_register_extra_handlers'
collect2: error: ld returned 1 exit status

This happened due to failure in including "includes.h" before checking
the above mentioned configure options.

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>