If you want to perform replication testing, then you need to install PostgreSQL with tcl. If you have not done so yet, then you can go through the installation steps again and use the following commands:
./configure --with-tcl gmake clean gmake gmake install
The make clean is only needed if you already ran the configure script before. If this is the first time you are running the configure script in this directory, then the gmake clean is not needed.