Set application root absolute path in magento
If you want to change the path of magento core application folder, then you can set it as:
Mage::setRoot('/path/to/your/app');
If you look into app/Mage.php you will find that function.
Magento - Force Display Full Breadcrumb Path
UPDATE: This was previous method that I used to force display full breadcrumbs for all product pages. Scroll to the bottom of the article to find new method which you can download from github as well.
Today's another issue with magento: not displaying full breadcrumb i.e. categories not included in path. I'm not overriding this time as very little time was assigned to fix this.