Function cli_safe_read not exported

Function cli_safe_read is very important for custom client software, which do read DB answer. Without this function you can not implement custom slave library:

https://github.com/dimarik/mysqlslave

Moreover, some other projects need it, for example Facebook's HipHop:
http://nareshv.blogspot.in/2011/10/building-facebooks-hiphop-on-fedora-15.html

It's easy to add cli_safe_read function to export list in libmysql/CMakeLists.txt