Experimental planner change to avoid a skip-scan if a regular index scan on

the same index columns can be done instead.

FossilOrigin-Name: 350f29ea1c577c5a46eee40e4b3cf4a022502e0c1dcb3ef1831a748069399232

diff --cc manifest
index ef8b42a231e514b48f1f4ac965473b30d4d4f5d7,3e7e1ec234b6692facfd9798445b955ae6a6d0fa..2202cf0ccc861df9f044eb2f4923af965d24d319
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Merge\sbegin-concurrent\schanges\sinto\sthis\sbranch.
- D 2018-07-10T15:48:39.705
+ C Experimental\splanner\schange\sto\savoid\sa\sskip-scan\sif\sa\sregular\sindex\sscan\son\nthe\ssame\sindex\scolumns\scan\sbe\sdone\sinstead.
 -D 2018-07-04T14:28:07.015
++D 2018-07-10T15:55:29.487
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F Makefile.in 0a3a6c81e6fcb969ff9106e882f0a08547014ba463cb6beca4c4efaecc924ee6
@@@ -581,10 -577,10 +581,10 @@@ F src/vdbesort.c 731a09e5cb9e96b70c394c
  F src/vdbetrace.c 79d6dbbc479267b255a7de8080eee6e729928a0ef93ed9b0bfa5618875b48392
  F src/vtab.c 10ea07dec111de6fb0a4fc87a7ffa4c65fdc088a19dbfaf7d6f2b128f2e8eb7b
  F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 -F src/wal.c d44a0811afd2155b1157c38b33141d4ac028fda6232485bed664015bb05819ca
 -F src/wal.h 8de5d2d3de0956d6f6cb48c83a4012d5f227b8fe940f3a349a4b7e85ebcb492a
 +F src/wal.c a49089219d0421ad172918ec8d7a3c637ee6f1c56026e45f0678073d9e346097
 +F src/wal.h 1713fefe4587678c295bbeb91c4e7442998ad74f19249869ce49dda9e8ce5d53
  F src/walker.c ba7225773931760cf60bf22f34d0cce2588df7ce5ce0f215a52eb88234b55ac4
- F src/where.c 0bcbf9e191ca07f9ea2008aa80e70ded46bcdffd26560c83397da501f00aece6
+ F src/where.c a38a485f36335c299f1810bcba11fa3cfe7ac10bc6148e4c13500a9c79d59219
  F src/whereInt.h b90ef9b9707ef750eab2a7a080c48fb4900315033274689def32d0cf5a81ebe4
  F src/wherecode.c 3317f2b083a66d3e65a03edf316ade4ccb0a99c9956273282ebb579b95d4ba96
  F src/whereexpr.c 571618c67a3eb5ce0f1158c2792c1aee9b4a4a264392fc4fb1b35467f80abf9a
@@@ -1759,7 -1746,10 +1760,10 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
  F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
  F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
  F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
- P be7004a971a174ae5c862cb3fa29f3586882d9ed1630d3e50e686d7310ccbc91 e9a3e8642e7acc8e63b35662ffae3a5a0da8d4f1ecefcb1db3110be19cbdab2b
- R 47be50798c4616a010a2e74703e49152
 -P 5a12db75d1da65daa92413a6b5892309e9d9479bb3610764e1015abe5bf28dbe
 -R d1c973cef7dd338d2474c5f688523a12
 -T *branch * exp-avoid-expensive-skipscan
 -T *sym-exp-avoid-expensive-skipscan *
 -T -sym-trunk *
++P af17432eb135895f9a55115c0eb364745715bb2dc14da01cbb2dc498e61c1853 32924446db0d07e5b2661a6626136a7bcdda629de23f98f3e1e862dd52d2f8a5
++R f2540424fa1966c3ffd1261f4537ae2b
++T *branch * exp-begin-concurrent-pnu
++T *sym-exp-begin-concurrent-pnu *
++T -sym-begin-concurrent-pnu *
  U dan
- Z 5dd9ea69c1fd7265f2be69ef45731b41
 -Z 68eb1d8d6b0bd6cc041bab15b5fea3f0
++Z e38693e9dae103965eb5d4da237ebd63

diff --cc manifest.uuid
index bef69445913b230b586f9dac6cf449a28fcb371b,98e9a2b0fc4a7f1e6511f5af09d3d79fbf2eae36..e88736145bc288340817f7cba4fc0021148bf230
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- af17432eb135895f9a55115c0eb364745715bb2dc14da01cbb2dc498e61c1853
 -32924446db0d07e5b2661a6626136a7bcdda629de23f98f3e1e862dd52d2f8a5
++350f29ea1c577c5a46eee40e4b3cf4a022502e0c1dcb3ef1831a748069399232