Purge bashisms, adduser, and addgroup from packages.git

See merge request adelie/packages!293

Package bumps for 20 July 2019.

See merge request adelie/packages!287

system/patch: patch(!) for CVE-2018-6952, 2019-13636, 2019-13638

See merge request adelie/packages!294

system/abuild: Fix URL

See merge request adelie/packages!292

system/s6-linux-init-early-getty: new subpackage of s6-linux-init

See merge request adelie/packages!291

system/adelie-base-posix: Depend on utmps

See merge request adelie/packages!290

Remove lvm2's device-mapper subpackages

See merge request adelie/packages!289

Bump user/php7 and user/php7-apcu

See merge request adelie/packages!288

user/subversion: add subversion-pl for git-svn support

See merge request adelie/packages!286

This makes the packages significantly saner, at the expense of pulling
in a few more MB worth of files for users who only need dmsetup or
libdevicemapper. Currently, it's not clear to users where the
development headers or man pages for these can be found, and there are a
few more minor annoyances such as the dmeventd openrc script not being
contained in an -openrc subpackage.

The /lib/libdevmapper.so symlink should be unneccessary, since there's
already a symlink in /usr/lib/.

Half the .so symlinks are in /lib/, while the other half is in
/usr/lib/, but imho fixing that isn't worth the hassle.