Still having problems with this?
As it says in the error message, you are not allowed to execute /usr/bin/patch, because your service provider uses open_basedir restriction.
The function is_executable returns false, and the plugin 'edit_patch' does not get loaded. This is the correct behaviour, I believe.
Have you enabled 'debug' mode in your Moodle (configuration/variables/debug). If not, the warning should not appear and mess with your headers. If debug has been set to 'No' and you still get the warning, you can remove it by adding an error control operator (@):
if (@is_executable( ...
Regards, Jarkko.