[DO NOT MERGE] Julia0.6 support

[oxinabox]

This is a PR to track julia 0.6 backports.

They will go onto version 0.4.x

Don't merge it.

[codecov-io]

Codecov Report

Merging #64 into master will decrease coverage by 18.77%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master      #64       +/-   ##
===========================================
- Coverage   81.75%   62.97%   -18.78%     
===========================================
  Files          12       12               
  Lines         148      235       +87     
===========================================
+ Hits          121      148       +27     
- Misses         27       87       +60

Impacted Files	Coverage Δ
src/resolution_automatic.jl	58.13% <100%> (-6.15%)	⬇️
src/util.jl	41.93% <0%> (-41.4%)	⬇️
src/resolution.jl	72.72% <0%> (-27.28%)	⬇️
src/post_fetch_helpers.jl	45.83% <0%> (-18.88%)	⬇️
src/fetch_helpers.jl	85.71% <0%> (-14.29%)	⬇️
src/verification.jl	86.66% <0%> (-13.34%)	⬇️
src/registration.jl	87.5% <0%> (-12.5%)	⬇️
src/locations.jl	87.5% <0%> (-6.25%)	⬇️
src/resolution_manual.jl	0% <0%> (ø)	⬆️

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[oxinabox]

Ok good that passed tests,
tagging a release on this branch.
called 0.4.3

[oxinabox]

released 0.4.3, with backported environment var name fix
JuliaLang/METADATA.jl#19393