FIX: Re-import externals/netcdf.py from scipy

[effigies]

Fixes deprecation error currently appearing in the pre-release Travis build.

Targeting 2.5.x first, since some Python 2 compatibility was removed in 3.0-dev. Once this is fixed, I'll use this diff to port to 3.0-dev.

This ends up overwriting incremental fixes put in netcdf.py since the last sync (#179), most notably #493. @rdvincent If you have any files you'd like to test that aren't in our battery, I would appreciate it to make sure we're not breaking MINC1.

@matthew-brett Do you remember if we have any fixes/hacks where we specifically chose to diverge from scipy?

[codecov]

Codecov Report

Merging #821 into maint/2.5.x will decrease coverage by 0.03%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           maint/2.5.x     #821      +/-   ##
===============================================
- Coverage        89.99%   89.96%   -0.04%     
===============================================
  Files               95       95              
  Lines            12049    12049              
  Branches          2143     2143              
===============================================
- Hits             10844    10840       -4     
- Misses             857      864       +7     
+ Partials           348      345       -3

Impacted Files	Coverage Δ
nibabel/openers.py	78.22% <0%> (-3.23%)	⬇️
nibabel/cmdline/parrec2nii.py	32.73% <0%> (ø)	⬆️

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[effigies]

Tests seem to pass, and the coverage drops seem unrelated.