[h323plus] h323plus Makefile fails to install all headers

Trying to build anything against h323plus, it quickly becomes obvious that there's a bug in the Makefile. It only installs include/*.h - not include/<subdirs>/*.h . So nothing will build, because h323.h references other headers from the subdirectories, which are not installed. This patch to Makefile.in makes it install the stuff from the subdirectories, resolving that problem. -- adamw