In practice, this should only matter when there are multiple
header files with the same name. That is something we try
to avoid already, by giving headers a distinct name.

When building NetworkManager itself, we clearly want to use
double-quotes for including our own headers.
But we also want to do that in our public headers. For example:

  ./a.c
    #include <stdio.h>
    #include <nm-1.h>
    void main() {
        printf ("INCLUDED %s/nm-2.h\n", SYMB);
    }

  ./1/nm-1.h
    #include <nm-2.h>

  ./1/nm-2.h
    #define SYMB "1"

  ./2/nm-2.h
    #define SYMB "2"

$ cc -I./2 -I./1 ./a.c
$ ./a.out
INCLUDED 2/nm-2.h

Exceptions to this are
  - headers in "shared/nm-utils" that include <NetworkManager.h>. These
    headers are copied into projects and hence used like headers owned by
    those projects.
  - examples/C

The numeric value of NM_SETTING_PROXY_METHOD_NONE should be zero,
as that is the more natural default.

Also, cast all uses of the enum values in g_object_set() to
(int).

Unnecessary APIs have been removed from nm-setting-proxy, client like
nm-connection-editor are expected to create a PAC script snippet the load
the location of file in NM.

libnm-core has been expanded to include proxy settings which clients
like nmcli, nm-connection-editor use to configure proxy in PacRunner. It
offers three modes i.e 'auto', 'manual'and 'none' and accordingly take
data to configure PacRunner. The modes matches on the PacRunner side too.