"nm-glib.h" is the most basic header, the one we cannot do without.
("nm-default.h", is already more generic, the one which every common
source file in NetworkManager repository should include).
Let "gsystem-local-alloc.h" be included by "nm-glib.h" and nowhere
else.
The "shared" directory contains files that are possibly used by all components
of NetworkManager repository.
Some of these files are even copied as-is to other projects (VPN plugins, nm-applet)
and used there without modification. Move those files to a separate directory.
By moving them to a common directory, it is clearer that they belong
together. Also, you can easier compare the copied versions to their
original via
$ diff -r ./shared/nm-utils/ /path/to/nm-vpn-plugin/shared/nm-utils/
