continuation of #109595
pkgconfig was aliased in 2018, however, it remained in
all-packages.nix due to its wide usage. This cleans
up the remaining references to pkgs.pkgsconfig and
moves the entry to aliases.nix.
python3Packages.pkgconfig remained unchanged because
it's the canonical name of the upstream package
on pypi.
This will make it easier to make overridable.
Had to rename `packages` attribute to `tools` in `php-packages.nix` because `packages` is shadowed by `makeScope`.
The first beta of php7 has been released. This enables developers to
test their code for breakage in preparation for the stable release and
allows us to make sure we don't have any bugs in the packaging prior to
the stable release.
