Expand project file names before storing them

Expand project file names before storing them

Before, whatever project-root returned, we stored as the root
directory of the project in project-list and project-list-file.  This
could lead to duplicate entries or bad behavior if projects were
accessed by different file names, e.g. both /home/user/src/emacs and
~/src/emacs.

Now project-list-file contains only expanded paths and project--list
contains only abbreviated paths.  We abbreviate filenames before
setting project--list, and expand filenames before writing to
project-list-file.  We only do this for local files, though, to avoid
making remote connections; the situation will still be bad for remote
projects, but at least this is an improvement.

* lisp/progmodes/project.el (project--write-project-list): Call
expand-file-name.
(project--read-project-list, project-remember-project)
(project--remove-from-project-list): Call abbreviate-file-name.