You can get the latest source code via Subversion:
svn co https://libyahoo2.svn.sourceforge.net/svnroot/libyahoo2 libyahoo2
This will create a directory called libyahoo2 in your current working directory.
To update your Subversion repository from within the libyahoo2 directory:
If you find bugs in the releases, try the latest Subversion trunk, some bugs are fixed in here.
To build the code from Subversion, first run the gen script. Then proceed with the normal configure, make, make install process.