Bug#992639: debianutils: move of installkernel to /usr/sbin/installkernel breaks kernel build on system with separate / and /usr

[Eric Valette]

I do not mind deciding everything should be in /usr but as pointed out 
there are other project that should adapt.

And for the sake of completeness, I already did merge. Just no 
remembered it! So even for merged / and /usr system there is a bug 
unless usrmerge is installed.

-- eric