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* Bug fixes:
- back out disabling the dependency resolver for single-package queries, it caused
too many regressions.
* Enhancements:
- allow explicitly disabling the dependency resolver via new environment variable,
PKG_CONFIG_MINIMUM_TRAVERSE_DEPTH=1. while pkgconf could already do this using
--minimum-traverse-depth=1, other pkg-config implementations do not have this
option, so adding an environment variable allows to make better use of this
feature (other implementations won't error due to unknown option this way)