Revise SSH config file forwarding.

This removes use of the ugly 'parsed-literal' box and [hopefully]
clarifies the instructions a bit.

Closes #46.
Merge branch 'master' into sean/fix-parsed-literal

Conflicts:
	manual/remote-access/gnu-linux/ssh.rst
	manual/remote-access/mac-os-x/ssh.rst
Merge pull request #53 from seanfisk/sean/fix-parsed-literal

Revise SSH config file forwarding.