[Yum] clarification of some yum.conf settings

[Robert P. J. Day]

  a few picky questions about the yum.conf man page:

1) do settings like cachedir and logfile have default values?
   it's not completely clear from "man yum.conf".

2) speaking of defaults, what about "exactarch"?  the man page
   does not state the default value for this setting.

3) should the explanation of "distroverpkg" be updated to reflect
   a default value of "fedora-release" instead of "redhat-release"?
   (given that, technically speaking, "redhat-release" is not the
   name of the package and therefore makes little sense as a 
   default value for this setting anyway).

rday