Fixes up scripts (except under /linux) to use `#!/usr/bin/env bash`
instead of `#!/bin/bash` or `#!/bin/sh` so that we don't end up with
the ancient version of bash supplied with macOS.
This became urgent with this PR, because of bash-4.xisms in
build-utils.sh, for example on line 572:
```
if [[ -v _builder_params[$e] ]]; then
```
Some of the global color variables in shellHelperFunctions.sh were a
little dangerously named. This cleans that up and removes a couple of
redundant functions from other locations.
mac/bashHelperFunctions.sh should be removed and replaced with
references to shellHelperFunctions.sh -- but I wanted to leave that for
a separate branch.
