Extensive edits to the comments in the sqlite.h.in source file to identify

testable statements of truth about the C-language interface.

FossilOrigin-Name: ea884e1ed8dba1aa0f3cf68fc71923954983f6c6

src/main.c

@@ -265,7 +265,7 @@ int sqlite3_config(int op, ...){
     /* Mutex configuration options are only available in a threadsafe
     ** compile. 
     */
-#if SQLITE_THREADSAFE
+#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0
     case SQLITE_CONFIG_SINGLETHREAD: {
       /* Disable all mutexing */
       sqlite3GlobalConfig.bCoreMutex = 0;