General config overrides mechanism and -c option for the cmdline

[mih]

Addresses #958

At present we have no simple way to test the few lines in main.py.

[mih]

Buildbot failure is due to the way the tests are executed there, i.e.

python -c 'import nose; nose.main()' -s -v datalad

it considers -c as sys.argv[0] and now there is an actual -c option in datalad. Can we use the same test invocation in the buildbots that we use on travis, i.e. via a call to nosetests? @yarikoptic

[codecov-io]

Codecov Report

Merging #1351 into master will decrease coverage by 0.07%.
The diff coverage is 92%.

@@            Coverage Diff             @@
##           master    #1351      +/-   ##
==========================================
- Coverage   89.22%   89.14%   -0.08%     
==========================================
  Files         237      237              
  Lines       24658    24678      +20     
==========================================
- Hits        22000    21999       -1     
- Misses       2658     2679      +21

Impacted Files	Coverage Δ
datalad/tests/test_config.py	100% <100%> (ø)	⬆️
datalad/config.py	98.58% <100%> (+0.02%)	⬆️
datalad/cmdline/main.py	76.02% <50%> (-0.74%)	⬇️
datalad/log.py	92.17% <0%> (-5.22%)	⬇️
datalad/crawler/nodes/matches.py	83.49% <0%> (-4.86%)	⬇️
datalad/tests/utils.py	88.41% <0%> (-1.13%)	⬇️
datalad/utils.py	89.1% <0%> (-0.39%)	⬇️

---

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[mih]

These changes are now a requirement for #1350.

[yarikoptic]

how come travis is happy and all buildbots aren't?

[mih]

@yarikoptic the answer is in the message above. And in #1353

[mih]

#1353 now merged into this one.

[mih]

OK, travis and buildbots (minus the ones with general trouble) are OK. Good to merge. Count down started. Veto?

[mih]

Gracie!