rename download script to download.sh

This is consistent with all the other shell scripts.
Do not hardcode cmake path
run-script.sh: cleanup
pkgs: disable 'make check' runs for most packages

These can take a loooong time, which is annoying while developing the
bundle. But of course ultimately they are also important, so at some
point we should turn this back on (or perhaps make it configurable; or
an extra, optional step between "build" and "install").
bundle: don't use the "PACKAGE" mechanism

Previously, there were broken fetch-bundle, build-bundle etc. targets.
Also, this isn't really a package.
Makefile: let all packages depend on 'bundle' target
bundle: cleanup
bundle: add gap.icns
gap: fix error in install.sh
add 'dmg' target creating disk image
Update README
bundle: update start scripts
common.mk: fix BASEDIR computation when included from deeper levels
Tweak 'make check' output, fix error when there are no hardcoded paths
common.mk: cleanup
gap: move GAP package build rules into separate "packages"
fix_install_names.sh: suppress install_name_tool warnings
gap: improve gap and gap package build rules
gap-pkgs: clean more temp files containing hardcoded prefix path
kbmag: make it possible to run build script a second time