Fixed an arithmetic error

Added Handful o' Hellfire Randomat event.

Added a new convar, ttt_clutterbomb_barrelschance, that can be used to configure how likely the Clutterbomb is to spawn explosive barrels instead of obstructive props.

You can set this value to 0 or 1 to make it never or always spawn explosive barrels respectively.

Set the value to any number between 0 and 1 to configure how likely it is to spawn the barrels. For example, the default value is 0.17 which means there's a 17% chance (about 1 in 6) of spawning the barrels.

The HUD help message at the bottom of the screen will update to reflect the convar but please note that this part will only take effect when the entity is reinitialised.