update to latest HEAD
    
    - Read FS yumvars before yum.conf setup, and reread if installroot changed.
    - Call systemd Inhibit, to inhibit shutdowns during transactions. BZ 1109930.
    - Have check provides check directly against the rpm index, and then quit.
    - Read env vars in readStartupConfig() to make them work in yum.conf. BZ 1102575
    - Add rules for naming files in /etc/yum/vars to yum.conf man page.