MELPA package fails to load when using package-quickstart

[yvie-k]

Installing the MELPA package when package-quickstart is enabled causes emacs to abort loading with the following error message:

Cannot open load file: No such file or directory, /home/<user>/.emacs.d/generic/proof-site

This error occurs early enough in the emacs startup phase that there will be no graphical window created. However, emacs -nw still kinda works (your emacs config isn't loaded though)

Steps to reproduce

1. Install the package from MELPA
2. M-x package-quickstart-refresh
3. Restart emacs
4. You get the error above

Cause

This is where the error occurs, because pg-init--pg-root is /home/<user/.emacs.d https://github.com/ProofGeneral/PG/blob/a894bcc5f915f1c76a2a83c12c12ea3497542426/proof-general.el#L69

pg-init--pg-root is defined here: https://github.com/ProofGeneral/PG/blob/a894bcc5f915f1c76a2a83c12c12ea3497542426/proof-general.el#L57-L64

Because it is loaded via package quickstart, load-file-name is /home/<user>/.emacs.d/package-quickstart.el instead of /home/<user>/.emacs.d/elpa/proof-general/proof-general.el