(ITS#3387) back-ldap and back-meta compile nits

[lukem-openldap@mewburn.net]

Full_Name: Luke Mewburn
Version: 2.2.17
OS: NetBSD
URL: ftp://ftp.openldap.org/incoming/luke-mewburn-041110.txt
Submission from: (NULL) (203.217.30.146)


ldap_back_open and meta_back_open are prototyped "extern" in the relevant
*/external.h files, yet "static" when implemented in the */back-xxx.c file.
This causes problems when compling with various compiler warnings enabled.

Other backends (e.g, back-ldbm, back-perl) don't declare the "XXX_back_open"
function a "static int", just "int", and don't suffer the same problem.

I've uploaded a patch with the trivial fix.