The --target option clashes with other command line flags and config files

[dstufft]

The --target option clashes with several other command like flags and config files like --user and distutils setup. Ideally we should handle this far more gracefully.

See also #3826, #4106, #562, #4139

[halms]

I have made an attempt to fix the behavior of --target in PR #4111.

[AlexeySanko]

#4111 was rebased to #4557

[jedie]

Current pull request is: #4557 isn't it?