issue748: Provide global variables for integrity check

Add global variables to the signature and hash verification tool to
ports/Makefile for use in the individual make templates.
issue748: Integrity check for bash

Add signature verification for bash downloads.
issue748: Integrity check for binutils

Add signature verification for binutils downloads.
issue748: Integrity check for coreutils

Add signature verification for coreutils downloads.
issue748: Integrity check for findutils

Add signature verification for findutils downloads.
issue748: Integrity check for gcc

Add signature verification for gcc downloads.
issue748: Integrity check for gdb

Add signature verification for gdb downloads.
issue748: Integrity check for lighttpd

Add signature verification for lighttpd downloads.
issue748: Integrity check for lynx

Prepare the integrity check integration for lynx. However, the current
source of the tarball does not contain the signature file. The official
location contains the signature. Thus, upon switching to the official
location, the signature check can be enabled.
issue748: Integrity check for make

Add signature verification for make downloads.
issue748: Integrity check for openssh

Add signature verification for openssh downloads.
issue748: Integrity check for vim

Add hash verification for vim downloads.
issue748: Integrity check for which

Add signature verification for which downloads.