Add projection function to find_* (and fix very bad bug)

[brjsp]

This started as an attempt to make find_* Ranges TS compliant (see #1668). But during testing, i discovered and fixed a bad bug in find_end making it unusable with custom comparison operator.
Because of this bug, i am making this pull request now, before writing a container version of the above algorithms. The regular versions are already usable as given in this pull request.

[hkaiser]

Thanks a lot!

Please also fix the inspect errors reported here: https://30382-4455628-gh.circle-artifacts.com/0/hpx_inspect_report.html

[brjsp]

After a discussion with @K-ballo on chat, i have removed plain find from the pull request, because it is really hard to do correctly (and in a way not requiring C++14).

[brjsp]

Actually doing a projection version of find_if and find_if_not would mean having to do also do this for the segmented algorithms, so not doing it now.

[hkaiser]

@brjsp thanks for working on this. I have not followed all the discussion around this - could you give a short overview about the current state of this PR, please?

[brjsp]

@hkaiser find_end and find_first_of have added projection and range version, the bug in find_end is fixed, other functions are untouched, should be ready for merging.

[hkaiser]

LGTM, thanks a lot!

[hkaiser]

@msimberg I think we can go ahead and merge this. There shouldn't be any interaction with other parts of HPX besides the algorithms themselves.

[msimberg]

@hkaiser yeah, this looks safe to merge. @brjsp could I just ask you to add hpx/parallel/container_algorithms/find.hpp here. Thanks a lot for your work!