Add support for FEATURES="protect-owned" which is identical to the

Add support for FEATURES="protect-owned" which is identical to the
collision-protect feature except that files may be overwritten if they are
not explicitly listed in the contents of a currently installed package.
This is particularly useful on systems that have lots of orphan files that
have been left behind by older versions of portage that did not support the
unmerge-orphans feature.

The additional tolerance makes this feature more suitable than
collision-protect for being enabled by default. In order to ensure smooth
operation of protect-owned in all cases, we also have to set
COLLISION_IGNORE="/lib/modules" since files inside this directory are
never unmerge. By enabling protect-owned by default, users are protected
from problems that may occur due interactions with file collisions and the
unmerge-orphans feature which is also enabled by default.

svn path=/main/trunk/; revision=11479