security/putty: update to 0.76.

FreeBSD relevant changes per
https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html

+ New option to abandon an SSH connection if the server allows you to

authenticate in a trivial manner.

+ Bug fix: user colour-palette reconfiguration via 'Change Settings'

were delayed-action.

+ Bug fix: server colour-palette reconfigurations were sometimes lost.
+ Bug fix: a tight loop could occur on reading a truncated private key

file.