Add the xInMutex method to the os-layer switch for testing whether or not

mutexes are used correctly. (CVS 2851)

FossilOrigin-Name: a582b159595ff8d31c81e9b3044711d6590d3f0e

src/os_unix.c

@@ -1586,6 +1586,16 @@ static void unixLeaveMutex(){
 #endif
 }
 
+/*
+** Return TRUE if we are currently within the mutex and FALSE if not.
+** This routine is intended for sanity checking only.  It is designed
+** for use in an assert() to verify that the mutex is held or not held
+** in certain routines.
+*/
+static int unixInMutex(){
+  return inMutex;
+}
+
 /*
 ** This function is called automatically when a thread exists to delete
 ** the threads SqliteTsd structure. 
@@ -1706,6 +1716,7 @@ struct sqlite3OsVtbl sqlite3Os = {
   unixCurrentTime,
   unixEnterMutex,
   unixLeaveMutex,
+  unixInMutex,
   unixThreadSpecificData,
   genericMalloc,
   genericRealloc,