Overhauled potions of blood and vampires.

1.) Vampires can only suck blood from creatures with M_COLD_BLOOD or M_WARM_BLOOD set (no insects anymore!)

These restrictions are the same for blood spatter.
Also, the monster's corpse must be of type contaminated (e.g. gnoll) 
or clean. Everything will be rejected.

2.) At xl 6 vampires gain the ability to create potions of blood from butchered corpses. The delay is the same as for butchering, and they also need a butchering tool (since I now think fangs don't really cut it); only the messaging is different, and the result, of course. If the monster doesn't meet the restrictions in (1), the corpse gets butchered instead (important when there are necromancers roaming about) and the resulting chunks don't get the THROWN flag set because vampires are unlikely to want to pick them up.

3.) Potions of blood can turn bad.

They last about 1200 turns which is a rather long time, though of course 
not infinite. Potions created from corpses take the corpse age into 
account. From age 199 downwards potions of blood are described as 
"congealed blood". The effect when quaffing is entirely the same, it's 
just a warning that the potion will soon disappear.

I've moved the potion descriptions over into item.plus, so that I could
use item.special for the timer to allow for easy comparison in 
update_corpses() etc.

Ideally each stack of potions of blood would have a props vector
attached (similarly to decks) with the timeout turns stored in order 
oldest to newest, so that you'd always drink the oldest potion first, and
if a potion was too old it (and it's time value) would just drop out of
the stack.
Since I haven't got this to work yet, instead the weighted average age
of two substacks is calculated and used for the combined stack. 
Congealed (age < 200) and comparatively fresh (age >= 200) potions of
blood will never stack.

As suggested in FR 191314, !blood are a now an additional power source for Sublimation of Blood, and the used potion turns into decay. And speaking of decay, I've modified the mummy curse to only affect a substack if the to-be-decayed potions are blood because I think losing your food source that way would be the equivalent of spores destroying all your food at the same time.

I think that's it; might still be buggy though I did test with some vampires, both wiz-mode and not, and because of the special -> plus change for potions, existing potions will now all look alike (clear potions).

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3626 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on March 13, 2008
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