setup: Ignore lxml on avg installation

[sils]

@NiklasMM if this is good to you you'll wanna add it to your cherry PR :)

[jayvdb]

This doesnt help the average user, as they use pip, and pip uses the whl's , and wheel's dont run setup.py.

#1476 would provide one way to do this, effectively marking some bears as 'use at your own risk'.

And of course #1000 will solve this properly. (But that is waiting on improvements to package_manager which nobody seems to wont to work on unless I crack the whip).

[sils]

This doesnt help the average user

It does, right now coala can't be installed without installing lxml via distribution and it gets the user a pretty mad looking error which isn't easy to understand.

With this we just don't install it by default, similar situation as language-check back then.

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Another story:

I'm actually looking at dependency_manager/package_manager right now because the build is broken due to an issue there that we never found yet but once I enabled the super() check_prerequisites check for linter we got lots of more testcases.

On linux this worked totally fine but on windows we get exceptions from dependency manager.

[AsnelChristian]

ack 125acf4

[AsnelChristian]

@rultor merge

[rultor]

@rultor merge

@AsnelChristian OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@AsnelChristian Done! FYI, the full log is here (took me 2min)