Description of problem:
In distros it is often necessary to have packages that only get installed
when certain other packages are installed or going to be installed.
For example langpacks for certain packages or input method support,
or cross-package support and features.  It would also be important
to people upgrading and getting new features installed that they might
otherwise not be aware of.

Steps to Reproduce:
1. Upgrade from F8 XFCE desktop to F9 with scim installed 
2. try to use scim in F9 xfce
  
Actual results:
2. Does not work since imsettings-xfce (new package) did not get installed.
Can't fix problem in comps, or yum without some hack.


Expected results:
2. If xfce-desktop could have a conditional dependency on imsettings-xfce
if imsettings is installed this would solve the problem and an update
could be released to fix it.

Additional info:
This would correspond to (and might remove the need for) condtional packages in
comps.