When a build fails, generate a status message showing which package

When a build fails, generate a status message showing which package
failed and the path of the relevant log file if available. Thanks
to _neuron_ for the suggestion. Here is some sample output:

 >>> Emerging (1 of 1) foo-bar/baz-1.0
 >>> Failed to emerge foo-bar/baz-1.0, Log file:
 >>>  '/var/log/portage/foo-bar:baz-1.0:20080814-202327.log'

svn path=/main/trunk/; revision=11411