Use CRON for re-generating sitemaps

It causes infinity redirect loop when running Cron via the website and not in Drush.
When checking -drupal_is_cli(), there should be another check if the path is cron.php

I changed the check from !drupal_is_cli(), to if ((strpos(current_path(), '/google_image_sitemap'))), so it works from the button in the module settings, and cron via drush/manually.

At first I couldn't apply the patch in #4, I could after adding an empty end of file line.

When applied, I got big load times in some pages, I solved it adding strict type comparison for the strpos() function. Like this:

if (strpos(current_path(), '/google_image_sitemap') !== FALSE) {

Also check the code standards for comments please! They are missing some dots at the end of the lines. I think everything is working correctly after applying these changes.

Applied patch from #4 and fix from #5. Sitemap generates but not update on RE-generate
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Sorry, it was caching, all work perfect)

Patch from #4 plus fix from #5 working well for me.

A bit more elegant way, and some code standards fixes

EDIT - A small typo, the next comment is the up-to-date works patch