Clean up the IN operator code generation logic to make it easier to reason

about.  In the process, improve code generation to omit some unused OP_Null
operations.

FossilOrigin-Name: 7c6fbcfe6ed5739e8e4639b7b123fbf9828cbfc0

diff --cc manifest
index f13081bfc1879e83ca2860e5cc2791c6916ef98f,76ab0745e9fd1b987b663d09b36e1f07dd9d8755..d534cb249b53bbeddd78c6d8fe9ee6ca7e1ff7fe
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Enhance\sthe\sPRAGMA\sintegrity_check\scommand\sto\sdetect\sUNIQUE\sand\sNOT\sNULL\nconstraint\sviolations.
- D 2014-08-01T01:40:33.869
 -C The\sidea\sof\scoding\sIN\soperator\swith\sa\sshort\slist\son\sthe\sRHS\sas\san\sOR\sexpression\nturns\sout\sto\sbe\shelpful.\s\sIf\sthe\slist\sis\sof\slength\s1\sor\s2,\sthe\sOR\sexpression\nis\svery\sslightly\sfaster,\sbut\sthe\sephemeral\stable\sapproach\sis\sclearly\sbetter\sfor\nall\slist\slengths\sgreater\sthan\s2.\s\sBetter\sto\skeep\sthe\scode\ssimple.
 -D 2014-08-01T15:34:36.551
++C Clean\sup\sthe\sIN\soperator\scode\sgeneration\slogic\sto\smake\sit\seasier\sto\sreason\nabout.\s\sIn\sthe\sprocess,\simprove\scode\sgeneration\sto\somit\ssome\sunused\sOP_Null\noperations.
++D 2014-08-01T15:51:36.528
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
  F Makefile.in 5eb79e334a5de69c87740edd56af6527dd219308
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@@ -1185,7 -1185,7 +1185,8 @@@ F tool/vdbe_profile.tcl 67746953071a9f8
  F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
  F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
  F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
- P e75b26ee357bb3d3c1a539b05d633ebf314726d7
- R 50d518176c08d9fef67243df4085599b
 -P ee0fd6aaf94cda1dce3fe752bfe3b0f83e0043f1
++P 9abcf2698c09f4f6a44a68e74f9f6b538f3253d6 e13175d3579e1045165bab091b3b28951d691704
+ R b49330a02feffafe84f051ae1dbb9076
++T +closed e13175d3579e1045165bab091b3b28951d691704
  U drh
- Z ae546b77e53655a859301e9ce422b440
 -Z f695386e744e4159654587b52ac0d789
++Z e21436d3fd2e7daacda65f50d724cf15

diff --cc manifest.uuid
index 087d6ad801bf216952967e44d66d15fcc32d531e,9b33d2f23a4eef889f7004c333274b95b4cdde57..06cf7d667373951178c24ca3f3408f385c212ea9
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 9abcf2698c09f4f6a44a68e74f9f6b538f3253d6
 -e13175d3579e1045165bab091b3b28951d691704
++7c6fbcfe6ed5739e8e4639b7b123fbf9828cbfc0