Fix list/kvlist objects not being cleared of default when reading config

This addresses REPOS_DIR in the PREFIX/etc/pkg.conf file not overriding
the defaults but causing it to instead append to them.

Fixes #680
Fix another segfault in pipeevent
Don't free(conf) when cleaning up LIST/KVLIST
Sync from libucl
Use ucl variable system to handle ${ABI}
Add a seat belt in pkg_config_value_free
Fix man page for option "pkg info -E"
Fix parse boolean value from config
Fix man page for option "pkg info -E". #2
Merge pull request #686 from svagner/master

Fix man page for option "pkg info -E"
Revert "Fix parse boolean value from config"

This reverts commit 57bccb7a540060ef3eb270cb272371a5219e91f9.
Tidy up the grammar a bit.  Update the 'last modified' date.