bitbake: adding a new comment should be placed on a new line

In this case, the comment is appended to the end of the file.
Some text editors, do not place  a '\n' to the end of the file
after saving it.

[YOCTO #4636]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake: python funcname can not include special character @

[YOCTO #4772]

When path:file change to python function, it maybe include '@' character.
So, add the special character to change to '_' for avoid error.

Signed-off-by: Li Wang <li.wang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
cookerdata: Improve message if BBPATH is unset and bblayers.conf not found

If BBPATH isn't set and bblayers.conf isn't found, improve the message
shown to the user to help their understanding of what the problem might
be.

[YOCTO #3271]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
A
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>