Throw an exception instead of doing a console.warn() when a plugin can't be found, to avoid mysterious errors later due to holes in the plugin array.   Refs #14437 !strict.
Throw an exception instead of doing a console.warn() when a plugin can't be found, to avoid mysterious errors later due to holes in the plugin array.   Refs #14437 !strict.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@27364 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful