CentOS 6.5 64bit support

Create a emulators/linux_base-c6_64 port for the 64bit version of CentOS 6.5

Update all of the linux-c6-* ports to support i386 (i686) or amd64 (x86_64)
Please abstract this into bsd.linux-rpm.mk - you have 46 instances of it in this pull request :-)