Log plugin activation errors.

dbg_act_log

<?php

// install it in mu-plugins
add_action('activated_plugin', 'dbg_log_error', 0, 2);

function dbg_log_error($plugin, $network_wide) {
	if (ob_get_length() == 0) {
		return ;
	}
	
	$buff = '';
	$buff .= "Plugin: $plugin\n";
	$buff .= sprintf("Network Wide: %s\n", $network_wide ? 'No' : 'Yes');
	$buff .= "Output:\n";
	$buff .= ob_get_contents() . "\n\n";
	
	file_put_contents(WP_CONTENT_DIR. '/plugin_activation_error.log', $buff, FILE_APPEND);
}