Introduce xbps_plist_{array,dictionary}_from_file().

Those are a wrapper around xbps_{array,dictionary}_internalize_from_zfile()
that prints a debugging msg when the plist file cannot be internalized.

Update xbps to use these wrappers.

bin/xbps-dgraph/main.c

@@ -598,7 +598,7 @@ main(int argc, char **argv)
 	if (conf_file == NULL)
 		conf_file = _DGRAPH_CFFILE;
 
-	confd = xbps_dictionary_internalize_from_zfile(conf_file);
+	confd = xbps_plist_dictionary_from_file(&xh, conf_file);
 	if (confd == NULL) {
 		if (errno != ENOENT)
 			die("cannot read conf file `%s'", conf_file);

bin/xbps-pkgdb/check.c

@@ -95,7 +95,7 @@ check_pkg_integrity(struct xbps_handle *xhp,
 		buf = xbps_xasprintf("%s/.%s-files.plist",
 		    xhp->metadir, pkgname);
 		assert(buf);
-		filesd = xbps_dictionary_internalize_from_zfile(buf);
+		filesd = xbps_plist_dictionary_from_file(xhp, buf);
 		if (filesd == NULL) {
 			fprintf(stderr, "%s: cannot read %s, ignoring...\n",
 			    pkgname, buf);