github issue #819 - magic harp vs shopkeeper

Issue reported by youkan700:  for shopkeepers, taming via magic harp
behaved differently than taming via scroll or spell.

Make magic harp's taming be the same as [non-cursed] scroll of taming
and spell of charm monster:  angry shopkeepers will be pacified (even
though they can't be tamed).

Also, add something I've been sitting on for ages:  when taming magic
hits an already tame monster, give that monster a chance to become
tamer.  Not significant for monsters that eat (unless being starved
for some reason) but matters for ones who don't eat.  For tameness N
(which has a maximum of 20), if N is less than 10, have any taming
yield a 10-N out of 10 chance to increase the tameness by 1.  So the
closer a pet is to becoming feral, the more likely for it to improve
tameness a little.

Closes #819

doc/fixes3-7-0.txt

@@ -965,6 +965,8 @@ out of array bounds access attempt occurred when deciding whether to bounce
 	if wand or spell zap reached edge of map
 if blind hero was challanged by a vault guard, it wasn't possible to see how
 	to start following that guard out of the vault
+make taming via magic harp be consistent with scroll of taming and charm
+	spell:  an angry shopkeeper becomes pacified (but never tamed)
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository
@@ -1731,6 +1733,7 @@ if built with DEBUG enabled and running in wizard mode, starting play with
 	water on Plane of Water, and fumaroles on Plane of Fire be transparent
 add wizard mode #wizkill command to remove monster(s) from play
 some quest nemeses release a cloud of poisonous gas when they die
+taming magic acting on an already tame creature might make it become tamer
 
 
 Platform- and/or Interface-Specific New Features