ICNS/JPEGTranslators: add Jamfile deps to lib headers

* Add Jamfile dependency to LIBPNG headers on icns_png.c;
* Add Jamfile dependency to LIBJPEG headers on JPEGTranslator.cpp
  be_jdatasrc.c

Conflicts:
	src/add-ons/translators/jpeg/Jamfile
boot loader tarfs: Declare dependency to zlib package
boot packagefs: Fix zlib dependency declaration
BuildHaikuPackage rule: Locate extract script

Missed that when adding the script. Therefore it would be created in the
current directory and when building multiple packages concurrently the
script would be overwritten.
HaikuDevel: Fix copying the build feature headers

We have to use actual targets that cause the respective download and
extract the packages. Otherwise the build fails when the packages
haven't been extracted yet.