Add a SELECTTRACE() macro to indicate when column names are assigned to

a SELECT statement.  This helps with debugging for tickets like
[de3403bf5ae5f72e] and [3b4450072511e621].

FossilOrigin-Name: 8f194008c3aaa4ef287200e37bc5278ba9c377a7091ee3f95bad66513226b083

manifest

@@ -1,5 +1,5 @@
-C In\sthe\ssqlite3TreeViewExprList()\sroutine,\sshow\sthe\s"AS"\salias\sname\sfor\s\neach\sexpression\sin\sthe\slist,\sif\sit\sexists.
-D 2017-12-22T19:53:02.654
+C Add\sa\sSELECTTRACE()\smacro\sto\sindicate\swhen\scolumn\snames\sare\sassigned\sto\na\sSELECT\sstatement.\s\sThis\shelps\swith\sdebugging\sfor\stickets\slike\n[de3403bf5ae5f72e]\sand\s[3b4450072511e621].
+D 2017-12-23T11:51:40.933
 F Makefile.in ceb40bfcb30ebba8e1202b34c56ff7e13e112f9809e2381d99be32c2726058f5
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 6480671f7c129e61208d69492b3c71ce4310d49fceac83cfb17f1c081e242b69
@@ -478,7 +478,7 @@ F src/printf.c 9506b4b96e59c0467047155f09015750cb2878aeda3d39e5610c1192ddc3c41c
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c bbee7e31d369a18a2f4836644769882e9c5d40ef4a3af911db06410b65cb3730
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
-F src/select.c 17e220191860a64a18c084141e1a8b7309e166a6f2d42c02021af27ea080d157
+F src/select.c 6c84733262885f70675b7b4d5c3f5d21562cd378cf06d5b0cb3bdbdb4785b85f
 F src/shell.c.in 339169a3d1307b5566ebe9ce15832d03439206106724c78cc3d9125a7b851795
 F src/sqlite.h.in 2126192945019d4cdce335cb236b440a05ec75c93e4cd94c9c6d6e7fcc654cc4
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1687,7 +1687,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 5c1fe6666019147a26480b5db1bf2f474a5d072c234c736f16ed5d2a9a040b3f
-R d3af759da34c77156099ceec10b188ae
+P 5efd854fe21470336ba4140294b6c90ef39af32e103b92c664438d7485c50f9a
+R 3deaa3da40d43e03f04500b413c136e7
 U drh
-Z f7d659c7910069dbd59e1c3feefe9c0a
+Z 1c7db6ece307b188f8e97c3dc484c292

manifest.uuid

@@ -1 +1 @@
-5efd854fe21470336ba4140294b6c90ef39af32e103b92c664438d7485c50f9a
+8f194008c3aaa4ef287200e37bc5278ba9c377a7091ee3f95bad66513226b083

src/select.c

@@ -1596,6 +1596,7 @@ static void generateColumnNames(
   if( pParse->colNamesSet || db->mallocFailed ) return;
   /* Column names are determined by the left-most term of a compound select */
   while( pSelect->pPrior ) pSelect = pSelect->pPrior;
+  SELECTTRACE(1,pParse,pSelect,("generating column names\n"));
   pTabList = pSelect->pSrc;
   pEList = pSelect->pEList;
   assert( v!=0 );