packages/pkgbuild: sanitize calling convention of all functions; rewrite pkgbuild_{need_,}update.

Calling convention: all functions, except interrogatory (specially commented),
take a path to the build directory, not path to PKGBUILD.

Rewrite: the case of existing, but not initialized, build directory is now handled
gracefully.
Also, nothing now relies on naming build directories after packages.
hooks/initscripts: ditch.
configs/globals: move definitions to scripts/* and load scripts before hooks.

- move
packages/export: check for rsync and git.
packages/fs: check for filesystem tools.
scripts/shell{,.utils}: rename to runner{,-parts}.
packages/{ask,text}: move to scripts.

They don't depend on external tools.
scripts/globals, framework: rip out the braindead so-called bootstrap (a canonical example of primitive overengineering). Stupid me.
packages/pkgbuild: pkgbuild_split_names: add a function for getting all pkgnames in a split package.