bug#68317: Can't sort *Packages* buffer by version after installing with package-vc

[Joseph Turner]

To reproduce:

1. Install some package using package-vc.

2. Open the *Packages* buffer: M-x list-packages.  The version column
for the newly installed package should display a git hash.

3. Click on the Version column header.  If the package's hash starts with
a letter, then instead of sorting the results, Emacs signals an error:

version-to-list: Invalid version syntax: 
‘c99367ebc2f0afe0baaf2f5e5ca1ad9d62ba6e21’ (must start with a number)

Thank you!!

Joseph