libxbps: added xbps_fetch_error_string(), that returns libfetch

fetchLastErrString.

Hook xbps-fetch to the tree and use the new function to print errors.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091030021303-6wu9sri5o8kgvfwl

lib/download.c

@@ -164,6 +164,12 @@ stat_end(struct xferstat *xsp)
 	    xsp->name, size, stat_bps(xsp));
 }
 
+const char SYMEXPORT *
+xbps_fetch_error_string(void)
+{
+	return fetchLastErrString;
+}
+
 int SYMEXPORT
 xbps_fetch_file(const char *uri, const char *outputdir)
 {