has_kit refactoring and related code

[jdevnull]

Modified has_kit to search all worn slots instead of just hold. When updating related code, also found and fixed two bugs:

• In do_treat, the variable i was first set as biotech skill, and then used as a counter to search equipment for a kit, before finally being used for the success test.
• In do_repair, using a vehicle workshop that is not a facility would result in a +4 TN penalty (as if the ch had no tools at all).

[luciensadi]

Looks good, thanks!