API headers are not found on non-default location

Passing the "lib" attribute downstream will allow to set
 -I/path/to/headers
to cc when checking the structure members and detection will
not fail if header is placed anywhere else than /usr/include

examples:

 - krb5.h is in /usr/include/kerberos5 directory on Solaris
 - ldap.h from openldap is in /usr/include/openldap/ because
   the /usr/include/ldap.h is from DS 5.0 (mozilla) C-SDK

In both cases all of the detections will fail if -Ipath is not passed.

--- a/buildtools/wafsamba/samba_autoconf.py	2013-06-13 09:21:02.000000000 +0000
+++ samba-4.1.7/buildtools/wafsamba/samba_autoconf.py	2014-06-10 11:53:22.567811902 +0000
@@ -439,7 +439,7 @@
 
 @conf
 def CHECK_STRUCTURE_MEMBER(conf, structname, member,
-                           always=False, define=None, headers=None):
+                           always=False, define=None, headers=None, lib=None):
     '''check for a structure member'''
     if define is None:
         define = 'HAVE_%s' % member.upper()
@@ -451,6 +451,7 @@
                       always=always,
                       headers=headers,
                       local_include=False,
+                      lib=lib,
                       msg="Checking for member %s in %s" % (member, structname))