scripts: csv.py: Enforced matching types in ternary branches

So in:

  $ ./scripts/csv.py input.csv -fa='b?c:d'

c and d must have matching types or else an error is raised.

This requires an explicit definition for the ternary operator since it's
a special case in that the type of b does not matter.

Compare to a 3-arg max call:

  $ ./scripts/csv.py input.csv -fa='int(b)?float(c):float(d)'      # ok
  $ ./scripts/csv.py input.csv -fa='max(int(b),float(c),float(d))' # error

scripts/csv.py

@@ -989,7 +989,11 @@ class RExpr:
     class IfElse(Expr):
         """b if a is non-zero, otherwise c"""
         def type(self, types={}):
-            return self.b.type(types)
+            t = self.b.type(types)
+            u = self.c.type(types)
+            if t != u:
+                raise RExpr.Error("mismatched types? %r" % self)
+            return t
 
         def fold(self, types={}):
             return self.b.fold(types)