Grenade activation warning messages.

 - shows red warning when activating grenades in Tactical. But...
   only works for Proxies in the preBattle equip screen (someone
   with more understanding of thinkers & timers might do it for the
   other grenades, on preTactical screen)

- 2 line change ( intended to replicate behavior of original )
Merge pull request #632 from kevL/gren_act_warn1

Grenade activation warning messages.