Revert "makepkg: additional conf. should be located in current directory"

This reverts commit b77810f25f6ca95dcbde22b4ac2327d5d0afffea.
Revert "makepkg: additional conf. is loaded after user's conf."

This reverts commit 2f1ff79a1c636411146dff10d8efc91c7452f4c3.
Revert "makepkg: load additional #makepkg.conf for $PACKAGE_FEATURE"

This reverts commit 99f165f75dc0a05604f01558157354c99b09771a.

Reason: We need to implement the feature in #s-makepkg instead.
Workflow:
  s-makepkg -> makepkg -> makepkg.conf -> [s pkgbuild_load] -> ...

Because [s variables] (here we need _FEATURE_STRING) is loaded after
[s pkbuild_load], we would load additional makepkg.conf *after* that.
This is not good. We need to load additional makepkg.conf inside the
[s pkgbuild_load].

We also need to create new tags to override the noisy tags 4.1.7, 4.1.8.