[PATCH 07 of 10 V5] rcutil: let environ override system configs (BC)

[Jun Wu]

Excerpts from Matt Harbison's message of 2017-04-07 23:14:20 -0400:
> That did the trick, thanks.  Out of curiosity, how did you figure you the  
> problem from that error message?  xargs would have been the last thing I  
> would have suspected.

I didn't figure it out from the error message - that's why I asked for your
environment to be able to reproduce.

The test is one big command piped together. I rewrote the pipe to use
temporary files. "hg locate" output differs - a couple of files were added.
Running check-code.py on added files showed no problem. Then I started to
suspect argv length limit.