Fix collectstatic tz handling

[jschneier]

No description provided.

[codecov-io]

Codecov Report

Merging #290 into master will increase coverage by 0.35%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #290      +/-   ##
==========================================
+ Coverage   72.52%   72.87%   +0.35%     
==========================================
  Files          10       10              
  Lines        1383     1379       -4     
==========================================
+ Hits         1003     1005       +2     
+ Misses        380      374       -6

Impacted Files	Coverage Δ
storages/backends/s3boto.py	88.19% <100%> (+1.78%)	⬆️

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[jschneier]

Fixes #49, Refs #141, #134, #84

Think this one is finally fixed for real, could use some help testing. Here are some people who previously expressed interest, should be quick to test:

@marcelchastain, @adam-thomas, @matheusjardimb, @dcloud, @mvanderlinde @CarlosBorroto

Going to merge in the next day or 2 so I can get a release out for Django 1.11 with get_modified_time in there.