[Guidelines change] Changes to the packaging guidelines

[Jason L Tibbitts III]

Here are the recent changes to the packaging guidelines:

The policy for systemd presets has been modified to merge the
individual treatments of service, socket and timer units into one
policy. The policy page was also moved into the packaging guidelines
proper.
 * https://fedoraproject.org/wiki/Packaging:DefaultServices
 * https://fedoraproject.org/w/index.php?title=Packaging%3ADefaultServices&diff=413672&oldid=413670
 * https://fedorahosted.org/fpc/ticket/532

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Slightly modified the per-product configuration guidelines to account
for changes in the os-release file.
 * https://fedoraproject.org/wiki/Packaging:Per-Product_Configuration
 * https://fedoraproject.org/w/index.php?title=Packaging%3APer-Product_Configuration&diff=411980&oldid=410805
 * https://fedorahosted.org/fpc/ticket/520#comment:7

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New guidelines for the consistent usage of SSL certificates by
applications have been added.
 * https://fedoraproject.org/wiki/Packaging:SSLCertificateHandling
 *  https://fedorahosted.org/fpc/ticket/480

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It is now mandatory that modules which support python3 be packaged for
python3.  Python modules which support both python2 and python3 may be
packages for both, or just python3.  Packaging of modules which support
only python2 are unaffected.
 * https://fedoraproject.org/wiki/Packaging:Python
 * https://fedoraproject.org/w/index.php?title=Packaging%3APython&diff=413621&oldid=409012
 * https://fedorahosted.org/fpc/ticket/526

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The AppData packaging guidelines have been updated to include
information about addon packages, and to use appstream-util instead of
appdata-validate.
 * https://fedoraproject.org/wiki/Packaging:AppData
 * https://fedoraproject.org/w/index.php?title=Packaging%3AAppData&diff=413661&oldid=398214
 * https://fedorahosted.org/fpc/ticket/527

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The R Packaging guidelines have been revised to indicate that the
DESCRIPTION file should not be marked %doc, as it is actually required
for operation of the R package and needs to be present even when
installed with --excludedocs.
 * https://fedoraproject.org/wiki/Packaging:R
 * https://fedoraproject.org/w/index.php?title=Packaging%3AR&diff=413668&oldid=234180
 * https://fedorahosted.org/fpc/ticket/535

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The BuildRequires section of the guidelines has been revised; the
exceptions list is gone.  The release engineering folks are free to
define the buildroot and rpm is free to change its dependency list.
 * https://fedoraproject.org/wiki/Packaging:Guidelines#BuildRequires_2
 * https://fedoraproject.org/w/index.php?title=Packaging%3AGuidelines&diff=413629&oldid=409506
 * https://fedorahosted.org/fpc/ticket/497