Merge the latest trunk changes, including the multi-threaded sorter, into

the sessions branch.

FossilOrigin-Name: d4cce2c71e64ab7b6a65a81b88b69445ed859351

tool/mkpragmatab.tcl

@@ -294,6 +294,8 @@ set pragma_def {
   IF:   defined(SQLITE_HAS_CODEC) || defined(SQLITE_ENABLE_CEROD)
 
   NAME: soft_heap_limit
+
+  NAME: threads
 }
 fconfigure stdout -translation lf
 set name {}

tool/mksqlite3c-noext.tcl

@@ -239,6 +239,7 @@ foreach file {
    malloc.c
    printf.c
    random.c
+   threads.c
    utf.c
    util.c
    hash.c

tool/mksqlite3c.tcl

@@ -255,6 +255,7 @@ foreach file {
    malloc.c
    printf.c
    random.c
+   threads.c
    utf.c
    util.c
    hash.c