bug#62621: 29.0.60; uniquify can't make buffers unique based on things other than filename

[Juri Linkov]

> - Hide the parent directory from the uniquification logic (only keeping the
>   project name). So that, for example, if I call 'M-x project-eshell' and
>   then 'C-u M-x project-eshell', the generated buffer names would not try
>   to use the parent segment to uniquify, and just stay as
>   <project-name>/*eshell* and <project-name>/*eshell-2*.

Often a project name in the buffer name is needed not for purposes
of generating a unique buffer name, but for permanent indication
which project a file/non-file buffer belongs to.

In such cases indeed a parent directory makes no sense,
but still uniquification is required for buffers inside
the same project, e.g.

  <project-name>/*eshell*<1>
  <project-name>/*eshell*<2>

So here are 2 styles combined: one for top-level project names
produced by project.el, and another style for the same project
by uniquify.el (in this case 'post-forward-angle-brackets').