has_interacted variable should not be bool

[qgeissmann]

it would be more convenient to have has_interacted as a small signed int. this way instead of being either:

• false -> no interaction
• true -> something has happended

we could have:

• 0 nothing has happened

• 0 discrete states describing interaction.

for instance a three way valve can be in two positions.

this should be backward compatible as if(0) == false & if(1) ==true.