[krbdev.mit.edu #6705] plugins don't build on HP-UX

[Arlene Berry via RT]

The problem is all of the Makefile.in's have the library extension
hardcoded to ".so":

 

                SO_EXT=.so

 

but they should be set to the DYNOBJEXT variable which is set to the
correct value by config/shlib.conf:

 

                SO_EXT=$(DYNOBJEXT)