re-implement pull req #334 - sorting discoveries

The pull request changed \ and ` output to unconditionally show
discoveries in alphabetical order.  That's nearly useless except
when looking at prediscovered weapons and armor that fighter
types start out knowing.

This allows the player to choose sorting order via the new
'sortdiscoveries' option.  In addition to setting it via
config file or 'O', it can be set via 'm' prefix for \ and `.
Choices are:
 o - sort by class, by order of discovery in class (default);
 s - sort by 'sortloot' classification which groups sub-class
     items (so all helmets before any other armor, then all
     gloves, then boots, and so on); within each sub-class, or
     whole class for classes which don't subdivide so usefully,
     partly-discovered types (where a name has been assigned)
     come before fully ID'd types;
 c - sort by class, alphabetically within class;
 a - sort alphabetically across all classes.

Turned out to be a large amount of work for fairly little gain,
although I suspect that 'sortdiscoveries:s' will eventually be
more popular than the default.

Invalidates existing save files so that current sort setting can
persist across save/restore cycles.

Closes #334

include/patchlevel.h

@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 28
+#define EDITLEVEL 29
 
 /*
  * Development status possibilities.