symset S_darkroom, S_vibrating_sqaure

Symbol set parsing rejected S_darkroom and S_vibrating_square.
Now it will accept them.

The fact that this bug wasn't noticed indicates that none of the
3.6.0 symbol sets (other than "Default symbols") is specifying a
value for either of these symbols.

This also changes the default vibrating square value from yellow
'^' (caret) to purple '~' (tilde).  I don't think there's any risk
of mistaking it for a long worm tail (brown '~') and it emphasizes
that it isn't really a trap.

doc/fixes36.1

@@ -198,6 +198,7 @@ when using the 'O' command for regexp options (autopickup exceptions,
 commands invoked by uppercase meta characters: M-A, M-C, M-N, M-O, M-R, M-T
 	were missing from '? c' list of game commands (dat/hh)
 tweak Baalzebub's lair and clean up the map display for it
+symbol set definitions didn't recognize S_darkroom and S_vibrating_square
 
 post-3.6.0: fix "object lost" panic during pickup caused by sortloot revamp
 post-3.6.0: more sortloot revisions
@@ -278,6 +279,7 @@ wizard mode ^G can now specify "male" or "female" when creating a monster
 REPRODUCIBLE_BUILD is new config.h setting to fetch build date+time from
 	environment instead of using current date+time, so that later rebuild
 	could duplicate the original (disabled by default; tested for Unix)
+default value for vibrating square symbol changed from yellow '^' to purple '~'
 
 
 Platform- and/or Interface-Specific New Features