more meaningful error message in ConfigStaticManifest.php (depth < 0)

Changed error from: Fatal error: Hmm - depth calc wrong, hit negatives in /var/www/tangoio.maori.nz/framework/core/manifest/ConfigStaticManifest.php on line 242 

... to .... 


Fatal error: Hmm - depth calc wrong, hit negatives, see: /var/www/mysite.maori.nz/mymodule/code/MyClass.php in /var/www/mysite.maori.nz/framework/core/manifest/ConfigStaticManifest.php on line 240

The first error is completely meaningless and impossible to debug...
Merge pull request #2470 from sunnysideup/patch-19

more meaningful error message in ConfigStaticManifest.php (depth < 0)