Enhance the query planner cost estimation for index scans to take into account

WHERE clause terms that can be computed using only the index and that do not
require looking up rows in the original table.  This fixes an obscure
performance regression that arose when the ORDER BY LIMIT optimization was
added by check-in [bf46179d44843].

FossilOrigin-Name: 9e2b26811452a5011d0a97a689636fa4409da856

diff --cc manifest
index 185e06b3cc8c6732a40abe59a253110f4877f2f1,b810c2000b086d406437fac2bf547fd9ac409985..d0e7b14e5400797b7c983af7137c90548a8dcbf9
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Initialize\sa\svariable\sin\swhere.c\sto\savoid\sa\svalgrind\swarning.
- D 2016-07-27T16:03:54.108
 -C Add\stest\scases\sand\sfix\sa\scomment.
 -D 2016-07-27T19:20:58.611
++C Enhance\sthe\squery\splanner\scost\sestimation\sfor\sindex\sscans\sto\stake\sinto\saccount\nWHERE\sclause\sterms\sthat\scan\sbe\scomputed\susing\sonly\sthe\sindex\sand\sthat\sdo\snot\nrequire\slooking\sup\srows\sin\sthe\soriginal\stable.\s\sThis\sfixes\san\sobscure\nperformance\sregression\sthat\sarose\swhen\sthe\sORDER\sBY\sLIMIT\soptimization\swas\nadded\sby\scheck-in\s[bf46179d44843].
++D 2016-07-27T19:30:53.586
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  F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
  F Makefile.msc d66d0395c38571aab3804f8db0fa20707ae4609a
@@@ -463,7 -463,7 +463,7 @@@ F src/vxworks.h d2988f4e5a61a4dfe82c652
  F src/wal.c 02eeecc265f6ffd0597378f5d8ae9070b62a406a
  F src/wal.h 6dd221ed384afdc204bc61e25c23ef7fd5a511f2
  F src/walker.c 0f142b5bd3ed2041fc52d773880748b212e63354
- F src/where.c 9981707ac01438baea5caa0ca6108237be6630da
 -F src/where.c 66a290310e71491ffc9c74108413176438aa8718
++F src/where.c 8ccc01f9227d41bfaf09360f108583be4a36d3b1
  F src/whereInt.h e5b939701a7ceffc5a3a8188a37f9746416ebcd0
  F src/wherecode.c 99707d11907c71d289ee9553d2d1a22f1fd8ba41
  F src/whereexpr.c d7dcbf14ce1b5876c1f76496162c30fcba669563
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+ U drh
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diff --cc manifest.uuid
index 83f63152b327323d139e609ed37f7ed61f591b03,213abdc7d34117921dab6f4efae2e30c4f063ab9..9b63447ecc8a34bd1df0e32ab49e9c4f229102fa
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 4d59df02d3713b3e3804e1a88e676749b2794286
 -50f8ea37fb9647c4a9da2c269a4d6f54b10ce96b
++9e2b26811452a5011d0a97a689636fa4409da856

diff --cc src/where.c
Simple merge