Quote arguments in aliases

[JordonPhillips]

This quotes arguments passed in to aliases.

I've run the tests for this on Windows in the following shells: git bash, powershell, cmd, and cygwin.

Fixes #2653
Also fixes #2657 (comment)

cc @jamesls @dstufft @kyleknap @stealthycoin

[codecov-io]

Codecov Report

Merging #2689 into develop will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #2689      +/-   ##
===========================================
+ Coverage    95.56%   95.57%   +0.01%     
===========================================
  Files          151      151              
  Lines        11801    11831      +30     
===========================================
+ Hits         11278    11308      +30     
  Misses         523      523

Impacted Files	Coverage Δ
awscli/compat.py	77.35% <100%> (+8.52%)	⬆️
awscli/alias.py	99.06% <100%> (ø)	⬆️

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[dstufft]

One tiny nitpick (that you can feel free to ignore), but I think I would prefer this to be r'\' (here and throughout) if only because it doesn't require mentally processing the escape to parse what this code is doing.

[JordonPhillips]

I would agree, but unfortunately r'\' isn't a valid string since the backslash can still escape quotes in raw strings. Really frustrating because it makes the tests hard to read.