Hmm nevermind. The param type had to be inout, but to do that the ctor
itself has to be inout. Somehow I managed to put the inout specifier
in the wrong place when testing, I did this:
this(inout(void*) obj) { } inout
which is not the same as this:
this(inout(void*) obj) inout { }
Damn specs. Anyway it's working ok now.