libtool (automake?) strange problem

[Xavier Décoret]

On one of my machine, a full build tree that otherwise works well, gives 
me the following weird problem:

shared libraries are installed without the .so extension ?!??!
Has anybody encountered this before? It used to work on this machine, I 
changed some stuff (that I cannot backtrace) and now it does not work 
anymore but it works on other machines ?!?!

PS: I am not doing any fancy stuff with libtool or whatsoever.