Allow humans to give a medikit to a teammate

[ppetr]

This could save lives :-), especially when running to base poisoned. Would encourage team play.

Variant: Allow to receive medikit only when the receiver has 100HP already. Variant: Heal - means use own medikit on someone else (my favorite now).

[ppetr]

Fixed. When using a medkit while these conditions hold:

• the user isn't poisoned,
• the teammate has lower HPs than the user

the medkit is used on the teammate