localhost ~ # nano /etc/portage/package.unmask
localhost ~ # emerge =x11-proto/xproto-7.0.10
Calculating dependencies... done!
!!! Error: the >=x11-proto/xproto-7.0.6 package conflicts with another package;
!!! the two packages cannot be installed on the same system together.
!!! Please use 'emerge --pretend' to determine blockers.
For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked