x86_64 is used as a baseline: the "x86_64" entry, whatever status it has,
is transformed into "all", and then the other entries in ARCHITECTURES
either dropped or rearranged appropriately.
Slayer
* Changes in summary/description
* Added REQUIRES
* Moved makefile_engine to BUILD_PREREQUIRES
* Removed mkdepend
* Sorted BUILD_PREREQUIRES
Sequitur
* Removed mkdepend
* Corrected copy command in INSTALL()
cp doesn't like -a when -L is used.
* Referring the current haiku version explicitly is not needed, since
the RequiresUpdater takes care of setting the version of Haiku used
for building a package.