Implement blueprint 'xbps-repo-list-via-cmdline'.

A new target (add-pkgidx) has been added to the xbps-repo command,
that takes two args, local repository dir and path to binpkg.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20090818121244-pfdagkfqeukn1t2r

bin/xbps-repo/index.h

@@ -27,5 +27,6 @@
 #define _XBPS_REPO_INDEX_H_
 
 int	xbps_repo_genindex(const char *);
+int	xbps_repo_addpkg_index(const char *, const char *);
 
 #endif /* !_XBPS_REPO_INDEX_H_ */