BUG: Fix NaT comparisons with Timedelta (#26039)

[ArtificialQualia]

• closes Comparing Timedelta and NaT gives inconsistent results depending on order #26039
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #26046 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26046      +/-   ##
==========================================
- Coverage    91.9%   91.89%   -0.01%     
==========================================
  Files         175      175              
  Lines       52485    52485              
==========================================
- Hits        48235    48231       -4     
- Misses       4250     4254       +4

Flag	Coverage Δ
#multiple	90.45% <ø> (ø)	⬆️
#single	40.77% <ø> (-0.11%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	75% <0%> (-12.5%)	⬇️
pandas/core/frame.py	96.79% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26046 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26046      +/-   ##
==========================================
+ Coverage    91.9%   91.97%   +0.06%     
==========================================
  Files         175      175              
  Lines       52485    52379     -106     
==========================================
- Hits        48235    48174      -61     
+ Misses       4250     4205      -45

Flag	Coverage Δ
#multiple	90.52% <ø> (+0.07%)	⬆️
#single	40.7% <ø> (-0.18%)	⬇️

Impacted Files	Coverage Δ
pandas/util/_doctools.py	0% <0%> (-12.88%)	⬇️
pandas/io/gbq.py	78.94% <0%> (-8.56%)	⬇️
pandas/core/indexing.py	90.53% <0%> (-0.35%)	⬇️
pandas/core/sparse/frame.py	95.49% <0%> (-0.21%)	⬇️
pandas/core/computation/engines.py	88.33% <0%> (-0.2%)	⬇️
pandas/util/testing.py	90.61% <0%> (-0.12%)	⬇️
pandas/tseries/holiday.py	93.1% <0%> (-0.11%)	⬇️
pandas/plotting/_core.py	83.76% <0%> (-0.11%)	⬇️
pandas/core/panel.py	35.43% <0%> (-0.1%)	⬇️
pandas/core/arrays/interval.py	93.06% <0%> (-0.06%)	⬇️
... and 68 more

---

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[pep8speaks]

Hello @ArtificialQualia! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-04-27 14:31:03 UTC

[jreback]

thanks @ArtificialQualia