Error generated in line 49 with function module_exist

Problem:
Installed thickbox against Drupal Head (5.0.1 Beta) and error is generated after enabling the Thinkbox setting for replacing image and thumbnails. The error generated is below:

Fatal error: Call to undefined function module_exist() in /home/themacge/public_html/welcome/sites/all/modules/thickbox/thickbox.module on line 49

Solution:
I do not know yet how to generate patches so here is the explanation:

In line 49 of thickbox.module the following line of code needs to be changed:
if (variable_get('thickbox_auto', 0) && module_exist('image')) {

New line should read:
if (variable_get('thickbox_auto', 0) && module_exists('image')) {

This seemed to fix everything and the module works as expected now.