data: Account for pre/postfunc functions when calculating dependencies

pre/postfuncs were not being added to checksums. This meant that when reconfiguration
occurred, tasks were not always being rerun when they should. This include
sstate functions as well as systemd's do_install function in the OE metadata.

With the addition of postfuncs, its possible a shell task can have a python
pre/postfunc so we have to guard against this when generating shell output
in emit_func.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
world-image: add extra target

* similar to world target, but collects all PACKAGES
* recipes marked with EXCLUDE_FROM_WORLD are excluded from world as well
  as world-image
* recipes marked with EXCLUDE_FROM_WORLD_IMAGE are excluded completely
  from world-image, sometimes you can build 2 recipes in same sysroot,
  but cannot install them in the same image
* PACKAGES listed in EXCLUDE_PACKAGES_FROM_WORLD_IMAGE are also
  excluded. You can remove e.g. ${PN}-dbg, but keep all other PACKAGES.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>