zlib.h in external causing build problem

[utensil]

@olavks reported that zlib.h in external is causing build problem at #48 (comment) .

This issue is to follow the problem.

[utensil]

It turns out that the problem is caused by the removal of zconf.h in #47 , and is missed by #97 .

Should recover:

• https://github.com/numenta/nupic/blob/46835bfdf53b4b2d12f88ed1fd0dd02f33bf22aa/external/common/include/zconf.h

• https://github.com/numenta/nupic/blob/46835bfdf5/external%2Flinux32arm%2Finclude%2Fzconf.h

• https://github.com/numenta/nupic/blob/46835bfdf5/external%2Flinux32armv7%2Finclude%2Fzconf.h

  to fix it.

[ghost]

The problem is that this approach is broken by design, as external libs that should never be included to begin with gets precedence and is included by default, even when building for Linux.
Also, breaking this to accomodate something that has 0,5% market share in HPC and breaking Linux with its 99% market share is not very sensible.

External libraries should never be included, period. If anything it should be put in contrib and/or have cmake deal with it.

This fix is only making the problem worse.

[utensil]

This issue started as #48 , when I encountered build problem on a Ubuntu which didn't have zlib development headers shipped with it and pre-installed. And in my personal development life, it's very rare to see development headers pre-installed on a system: zlib is most likely installed but not its development headers. Just as in #48 , I have to fix it manually by sudo apt-get install zlibc zlib1g zlib1g-dev.

When I started trying to address #48 , I was not aware of the way nupic handling external dependencies(including them not declaring dependencies) and soon noticed so. Though I personally dislike the way of including external libraries, I can figure out a few reasons and adapt to the convention.

My fix #97 is merely a patch to fix #48 , but not to dramatically change the convention, which require a proposing and voting process described on wiki, and I believe it would possibly break the build on Raspberry Pi or so, which I would not consider it as a 0.5% market share for AI developers.

You're welcome to propose the removal of external libraries on the mailing list, and if the motion passes, it would be great to have you work on PRs removing them without breaking things.