Fix PyInstaller support

[yagebu]

PyInstaller+Babel was supported for quite a while before 2.5.0 - which broke support for this configuration by default. PyInstaller actually synthesizes a __file__ for frozen aka bundled code that makes this "just work".

Closes #529.

[codecov-io]

Codecov Report

Merging #533 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #533      +/-   ##
==========================================
- Coverage      90%   89.99%   -0.02%     
==========================================
  Files          24       24              
  Lines        4024     4018       -6     
==========================================
- Hits         3622     3616       -6     
  Misses        402      402

Impacted Files	Coverage Δ
babel/core.py	95.51% <100%> (ø)	⬆️
babel/localedata.py	95.45% <100%> (-0.24%)	⬇️

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[yagebu]

Pinging @akx: Is anything blocking this from getting merged?

[akx]

Hi @yagebu – I'm so sorry I dropped the ball on this one! Merging now and releasing 2.5.2 thereafter.