Merge branch 'improve-environment-manipulation' into improve-environment-manipulation-update

Incorporate latest master in order to resolve test failures
that we will otherwise introduce due to the recent merge of
'test-cmake-generate-launcher-config'.

* improve-environment-manipulation:
  BUG: Fix problem when no extra paths set
  BUG: Make environment commands actually work
  STYLE: Avoid gratuitous stack variables
  BUG: Fix quoting of environment variables
  ENH: Add --launcher-show-set-environment-commands
  STYLE: Make ctkAppLauncherConfigure a function
  BUG: Don't add '.' to paths via wrapper script
  ENH: Support additional path list envvars
  STYLE: Simplify building path lists
  STYLE: Refactor platform conditionals
  BUG: Don't add '.' to PATH, LD_LIBRARY_PATH, etc.
BUG: Resolve test failures

Resolve failures in new tests that were added by the
'test-cmake-generate-launcher-config' branch, that are broken by changes
on this branch.
ENH: Add unit tests for additional paths feature

Modify the new configure unit test from the other branch to also test
the new additional paths feature.