relative sibling spacing for reviews

Anki 1.0 had a similar feature but we do things a bit differently now. The
relative spacing applies only to reviews, and spaces cards according to their
interval, instead of spacing all cards the same. Any delay < 1 full day is
treated as no delay, so with the default 10% setting, reviews with an interval
< 10 days are not spaced at all. This should hopefully cut down on support
queries for people wondering why many of their cards were delayed, allows the
two settings to be documented separately, and does away with the somewhat
confusing usage of non-integer new sibling values to disable review spacing.

anki/deck.py

@@ -164,7 +164,7 @@ class Deck(object):
         self.lastSessionStart = 0
         self.queueLimit = 200
         # if most recent deck var not defined, make sure defaults are set
-        if not self.s.scalar("select 1 from deckVars where key = 'latexPost'"):
+        if not self.s.scalar("select 1 from deckVars where key = 'revSpacing'"):
             self.setVarDefault("suspendLeeches", True)
             self.setVarDefault("leechFails", 16)
             self.setVarDefault("perDay", True)
@@ -184,6 +184,7 @@ class Deck(object):
 \\begin{document}
 """)
             self.setVarDefault("latexPost", "\\end{document}")
+            self.setVarDefault("revSpacing", 0.1)
         self.updateCutoff()
         self.setupStandardScheduler()
 
@@ -464,6 +465,7 @@ where type >= 0
         # spacing for delayed cards - not to be confused with newCardSpacing
         # above
         self.newSpacing = self.getFloat('newSpacing')
+        self.revSpacing = self.getFloat('revSpacing')
 
     def checkDailyStats(self):
         # check if the day has rolled over
@@ -832,23 +834,22 @@ limit %s""" % (self.cramOrder, self.queueLimit)))
 
     def _spaceCards(self, card):
         new = time.time() + self.newSpacing
-        # space reviews too if integer minute
-        if self.newSpacing % 60 == 0:
-            lim = "between 1 and 2"
-        else:
-            lim = "= 2"
         self.s.statement("""
 update cards set
 combinedDue = (case
-when type = 1 then :cut
+when type = 1 then combinedDue + 86400 * (case
+  when interval*:rev < 1 then 0
+  else interval*:rev
+  end)
 when type = 2 then :new
+else combinedDue
 end),
 modified = :now, isDue = 0
 where id != :id and factId = :factId
 and combinedDue < :cut
-and type %s""" % lim,
+and type between 1 and 2""",
                          id=card.id, now=time.time(), factId=card.factId,
-                         cut=self.dueCutoff, new=new)
+                         cut=self.dueCutoff, new=new, rev=self.revSpacing)
         # update local cache of seen facts
         self.spacedFacts[card.factId] = new