Improve result sampling in case we have too generic keywords

Instead of either displaying the exact match if we have only
one keyword and nothing otherwise, lets try to give people
a sample of results, on the chance that might still be useful.

Mostly just display the first 100 package names found (i.e.
from suffix entries that had no "too many prefixes" value).
Allow suffix entries with "too many prefixes" value to specifiy
if the empty prefix was contained in the set (that effectivly
avoids a regression in the case "single keyword, exact match
exists").

If in doubt, prefer package names that begin with the first
keyword and only abort if we have more than 100 of those
(The worst case behaviour of this should be very limited
to due the "too many prefixes" constraints).