Various bugfixes to spellbook screen.

Arcane and Divine tabs did nothing for a multiclass character.  They're
slightly functional now, with the possibly unwanted side effect of letting
spells per level count separately for arcane versus divine.  Multiclassing
still needs a lot of work; spellcaster code checks player level, not class
level, so a wizard 1 / cleric 1 has the spellcasting of a wizard 2 + cleric 2.

Disallow right-clicking to reduce the number of spells prepared below 0.

Tabs and spells per level were as wide as the dialog, which meant they
overlapped (and prevented the use of) the alphabetized spell list.

Charges display was too narrow, which meant it didn't display for some spells
(like a wizard's Summon Monster I).

Clicking on the alphabetized spell list caused an error, because fct was
unimplemented.  I implemented a simple fct to behave the same as clicking on a
spell's icon.  More cleanup would be good; it would be nice if the
alphabetical spell list and by-level spell list weren't in such different
formats, so code could be more easily reused.
Fixes for Animal Empathy and Diplomacy.

Using the skill on an invalid target no longer wastes a turn.

Befriending a target no longer resets the AI of every creature on the level.

Slightly more useful messages.

Using Diplomacy on yourself made everyone your friend.  Although very amusing,
this is now fixed.  Animal Empathy may need a similar fix if something like
wild shape ever changes the player's type.
Clean up character tooltips.

Delete tab characters in tooltips.  These were showing up as blocks because
the font didn't recognize them.

Show fractional CRs as fractions (like "1/6") instead of decimals ("0.1666667").
Merge pull request #141 from joshkel/bugfixes

Bugfixes