[libsmi] yang.h missing after install

Hi,

I've just tried building the current svn trunk in order to enable libsmi support in wireshark, and noticed that the installed include/smi.h has an include for yang.h, but yang.h isn't being copied to the specified include directory causing the build test in wireshark's configure script to fail and I've had to manualy copy yang.h to my /usr/local/include/ directory. This issue occurs regardless of specifying --enable-yang or not

Cheers, Wes