Made prefix delete trigger schema aware
Made prefix delete trigger schema aware

The trigger function which is executed before all delete operations in
the ip_net_plan table was not schema aware, which made it disallow
deletion of assignments having hosts in other schemas. This is now
fixed.

Fixes #156

SoundGoof/NIPAP,bbaja42/NIPAP,SpriteLink/NIPAP,plajjan/NIPAP,garberg/NIPAP,ettrig/NIPAP,SoundGoof/NIPAP,plajjan/NIPAP,fredsod/NIPAP,fredsod/NIPAP,bbaja42/NIPAP,garberg/NIPAP,fredsod/NIPAP,fredsod/NIPAP,fredsod/NIPAP,plajjan/NIPAP,SoundGoof/NIPAP,fredsod/NIPAP,SoundGoof/NIPAP,bbaja42/NIPAP,ettrig/NIPAP,plajjan/NIPAP,SoundGoof/NIPAP,bbaja42/NIPAP,ettrig/NIPAP,garberg/NIPAP,SpriteLink/NIPAP,garberg/NIPAP,bbaja42/NIPAP,ettrig/NIPAP,SpriteLink/NIPAP,plajjan/NIPAP,plajjan/NIPAP,garberg/NIPAP,garberg/NIPAP,ettrig/NIPAP,SpriteLink/NIPAP,SoundGoof/NIPAP,ettrig/NIPAP,SpriteLink/NIPAP,bbaja42/NIPAP,SpriteLink/NIPAP