Notice that there are two problem scenarios and two solutions.
Problem scenario: When installing Git on CentOS you get this error "http-push.c ... fatal error ... expat.h: No such file or directory"
Run this: yum install expat-devel
Problem scenario: When running commands to install Git on CentOS, you use the "make" command. But you get this error: "git-compat.util.h:...: fatal error: openssl/ssl.h No such file or directory."
Run this: yum install openssl-devel
Finally, for some good directions for installing Git 2.x on CentOS, see this link: http://tecadmin.net/install-git-2-x-on-centos-rhel-and-fedora/