Glass shards

Closes #4135.

* Adds glass shards as an extremely poor choice of melee weapon
* Adds a new item flag, HURT_WHEN_WIELDED, which has a 66% chance of hurting the user's hands when an attack is made with it. (Will be blocked by armor)
  * Adds the flag to the circular sawblade as well
* Glass shards are dropped by:
  * Breaking windows (domestic or otherwise)
  * Breaking windshields (normal and reinforced)
* Also makes reinforced windshields drop wire when broken into pieces