Re: housekeeping changes

[bill-auger]

some suggested tweaks to the tweaks (WRT the
'refactor-into-functions' branch)

fetch_source-check-existence-after-verify.patch:
* the changes in fetch_source() introduced a bug - if the
  "Removing existing invalid Firefox tarball" branch is taken, no
  source-ball would be present after fetch_source() returns


validate_env-local-vars.patch:
* give local scope to all function-specific variables, and
  remove the unused variable

fetch_source-check-existence-after-verify.patch
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validate_env-local-vars.patch
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