Modify feature_not_found to accept an optional second parameter to be
printed after the generic feature not found error.

Modify most calls to feature_not_found to provide hints as to the
packages that may be missing. The few calls remaining without a remedy
are ones I couldn't work out how to remedy myself.
Signed-off-by: NStewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>