Use standard errno codes in return from _alpm_archive_fgets

Use standard errno codes in return from _alpm_archive_fgets

This allows us to not require the context (e.g. handle) when calling
this function. Also beef up the checks in the two callers of this
function to bail if the last return code is not ARCHIVE_EOF, which is
the expected value.

This requires a change to one of the pactest return codes and the
overall result of the test, but results in a much safer operating
condition whereby invalid database entries will stop the operation.

Signed-off-by: Dan McGee <dan@archlinux.org>