Fix multiple integer overflows in expat.

Security: CVE-2015-1283
Security: FreeBSD-SA-15:20.expat

Fix make(1) syntax errors when upgrading from 9.x and earlier.
[EN-15:11]

Fix incorrect netstat(1) data handling on 32-bit systems.
[EN-15:12]

Allow size argument to vidcontrol(1) for syscons(4). [EN-15:13]

Approved by: so