reintroduce "check for leftovers if make package failed"

[Oliver Lehmann]

Hi, 

I once added a feature which made tinderbox check for leftovers even if make 
package failed (for example because you've specified to much files in 
pkg-plist). This avoids rebuilding the port once more after you cleaned up 
the pkg-plist just to see the new files after an upgrade. With that patch 
you a) get the files you've to much in your pkg-plist and b) the files which 
are missing. 

This was introduced in 1.19 of lib/buildscript, and got removed in 1.24. 

Patch is: 

http://pofo.de/tmp/buildscript.diff