Fix most shellcheck warnings in newvers.sh

[arichardson]

Summary

I did not fix the warning that "local" is undefined in POSIX sh since that
seems to be supported by /bin/sh on both FreeBSD and macOS

[emaste]

Using $( ) instead of ` is an improvement IMO, I'm a little less convinced by some of the new quote use.

sys/conf/newvers.sh

196

The quotes here seem confusing.

275–292

p4 section has been removed

[markj]

This file is pretty inconsistent about the use of braces around variable names; I prefer not to use them unless they're needed, like on line 299 in the new version.

sys/conf/newvers.sh

228

Does it not complain about the missing quotes around $svnversion?

[markj]

In D18569#414665, @emaste wrote:

Using $( ) instead of ` is an improvement IMO, I'm a little less convinced by some of the new quote use.

Agreed. I'm not a big fan of quoting every variable expansion, but it doesn't hurt.

[arichardson]

sys/conf/newvers.sh

196

"$(realpath ${0})" or completely omit them?

228

No warning. Either it assumes there can't be any spaces or it doesn't print the warning for non-arguments.

275–292

Will rebase shortly.