Rework the Horn of Geryon as an xp-charged evocable.

Previously the horn was a nearly useless item after unbarring the hells and
possibly opening a trove.  This version keeps the summon hell beast theme
but turns it into a more useful xp-charging evocable.  Evoking it when it's
charged summons 1-4 hell beasts, depending on evocations, each summon
having a small chance of being hostile, also depending on evocations.  The
chance of getting a hostile hell beast is 7 in evocations * 10 (always
hostile at evocations 0).  Two hell beasts get created 63% of the time at
10 evocations, three 63% of the time at 15 evocations, and 4 66% of the
time at 20 evocations, with always 4 summoned at higher than 23 evocations.

It could perhaps use an additional effect, but it's an always-generated
item that's relatively accessible in a 3-rune game, so some care has to be
taken there.

1 files changed, 1 insertions, 1 deletions

diff --git a/crawl-ref/source/effects.h b/crawl-ref/source/effects.h
index 3aa4926695..2eb9bd2330 100644
--- a/crawl-ref/source/effects.h
+++ b/crawl-ref/source/effects.h
@@ -66,7 +66,7 @@ bool vitrify_area(int radius);
 void update_level(int elapsedTime);
 void handle_time();
 void recharge_rods(int aut, bool floor_only);
-void recharge_elemental_evokers(int exp);
+void recharge_xp_evokers(int exp);
 
 void slime_wall_damage(actor* act, int delay);