Implemented a cache to get pkg dicts from metadir.

This improves xbps-pkgdb -a marginally, but still seems to be a bit slow.

lib/plist.c

@@ -264,40 +264,3 @@ xbps_array_replace_dict_by_pattern(prop_array_t array,
 {
 	return array_replace_dict(array, dict, pattern, true);
 }
-
-prop_dictionary_t
-xbps_pkgd_from_metadir(struct xbps_handle *xhp, const char *name)
-{
-	prop_dictionary_t pkgd, plistd = NULL;
-	const char *savedpkgname;
-	char *plistf;
-
-	assert(name != NULL);
-
-	savedpkgname = name;
-	plistf = xbps_xasprintf("%s/.%s.plist", xhp->metadir, name);
-
-	if (access(plistf, R_OK) == -1) {
-		pkgd = xbps_find_virtualpkg_dict_installed(xhp, name, false);
-		if (pkgd == NULL)
-			pkgd = xbps_find_pkg_dict_installed(xhp, name, false);
-
-		if (pkgd != NULL) {
-			free(plistf);
-			prop_dictionary_get_cstring_nocopy(pkgd,
-			    "pkgname", &savedpkgname);
-			plistf = xbps_xasprintf("%s/.%s.plist",
-			    xhp->metadir, savedpkgname);
-		}
-	}
-
-	plistd = prop_dictionary_internalize_from_zfile(plistf);
-	free(plistf);
-	if (plistd == NULL) {
-		xbps_dbg_printf(xhp, "cannot read from metadata %s for %s: %s\n",
-		    plistf, savedpkgname, strerror(errno));
-		return NULL;
-	}
-
-	return plistd;
-}