buildsteps.sh:  look for tcl/tkConfig.sh in /usr/lib64

LinuxCNC's configure.in needs update with RH locations
master.cfg: run buildsteps.sh with bash

The 'buildsteps-script' step doesn't preserve execute permissions on
buildsteps.sh, so explicitly run the script with bash.
HOW-TO-local-git-repo:  add forgotten 'git update-server-info' command

This is obviously an afterthought, and needs to be rewritten after
building the repo from scratch so that the order of steps can be
correctly explained.