Add zchunk support

[jdieter]

This patchset adds zchunk support to librepo. It requires that libsolv also have zchunk support enabled, and, for it to be effective, the calling application needs to pass the handle a cache directory to find old zchunk files to delta against (I've submitted a patch to dnf).

[jdieter]

Do please note, that, unlike the libsolv and dnf patches, these patches make zchunk a mandatory dependency. If you'd rather it be an optional dependency, please let me know.

[Conan-Kudo]

@jdieter I suspect that it might be desired for the RHEL side of the house to be optional, but I don't see a reason why we wouldn't want it on in Fedora and Mageia.

[j-mracek]

Without a merge of patch for libsolv it will not work?

[jdieter]

That's correct. It will download the zchunk metadata, and send it to libsolv, but without openSUSE/libsolv#270, libsolv won't be able to read the zchunk metadata.

[ignatenkobrain]

this should be pkg_check_modules

[dmach]

zck.h should #include <stdbool.h> as the boolean type is part of public header

There are also couple compilation errors, such as:
/usr/include/zck.h:62:29: note: expected 'zckCtx *' {aka 'struct zckCtx *'} but argument is of type 'int'
librepo/downloader.c:1089:11: error: too few arguments to function 'zck_init_adv_read
librepo/downloader.c:1156:31: error: too few arguments to function 'zck_init_read'
librepo/downloader.c:1208:29: error: too few arguments to function 'zck_get_range_char'

• tested with zchunk-devel-0.9.7-2.fc29

I also created PR to make zchunk optional - it's very important to us so we can turn it off on as needed:
jdieter#1

[jdieter]

Ok, I've gone ahead and merged your PR and added <stdbool.h> to zck.h in zchunk-0.9.10. This now compiles fine with zchunk-0.9.10+, but it won't work with repositories generated using the current createrepo_c zchunk patches because of the format changes.

[jdieter]

@dmach, If you'd prefer these to be in fewer commits, I'll squash them down for you

[Conan-Kudo]

@jdieter Could you please do so?

[jdieter]

@dmach, @Conan-Kudo is there anything else you need me to do on these before review?

[Conan-Kudo]

Use pkgconfig(zck) >= 0.9.11 here.

[Conan-Kudo]

Looks good to me.

[jdieter]

Thanks!

[Conan-Kudo]

@dmach, @j-mracek: This is now merged into libsolv, so can we get this reviewed and merged, as well as the corresponding PRs for the other components of the stack (as well as createrepo_c)?

[jdieter]

Is there anything else you need from me before you review this?