This patch rectifies
- packagemeta::ScanDownloadedFiles (package_meta.cc), and
- packagemeta::trustp (package_meta.h)
Clarification:
Class packagemeta has "fields" prev, curr, exp and installed, which in fact
represent the info from setup.ini/installed.db, and should never be cleared
therefore. _Currently_ these fields are cleared in ScanDownloadedFiles() in
order to notify that the tarball for the associated field is not available.
This is a mistake, as it destroys relevant info (e.g. the version number of
a version).
To ascertain whether or not the associated tarball is available, one should
invoke <field>.accesible().