Optimize: shorter sub definitions; drop true/false constants

Optimize definitions of subs:
- single expression without 'return'
- drop usage of 'true' and 'false' constants
- use 'scalar' around =~ for correctness

Drop constant definitions 'true' and 'false'
Inject Scalar::Util early; use "package _;"

Use 'package _;' to set the default package for compilation.

Inject Scalar::Util subs early during compilation to be able to use our
own names unprefixed in our own _::is_* subs definitions.
Applied perltidy to pull request
Merge branch 'pull-gh-1'