Avoid file descriptor leakes (fix #303)

HTTP connections are cached for performance, but they end up being
leaked when running configure scripts. To avoid this, close the
connection cache after all downloads are finished.

Closes: #326 [via git-merge-pr]

lib/transaction_commit.c

@@ -104,6 +104,12 @@ xbps_transaction_commit(struct xbps_handle *xhp)
 		goto out;
 	}
 
+	/*
+	 * After all downloads are finished, clear the connection cache
+	 * to avoid file descriptor leaks (see #303)
+	 */
+	xbps_fetch_unset_cache_connection();
+
 	/*
 	 * Collect files in the transaction and find some issues
 	 * like multiple packages installing the same file.