Do not enable lazy locking by default.

Do not enable lazy locking by default, because:
- It's fragile (applications can subvert detection of multi-threaded
  mode).
- Thread caching amortizes locking overhead in the default
  configuration.
diff --git a/INSTALL b/INSTALL
index fa32d05..a210ec5 100644
--- a/INSTALL
+++ b/INSTALL
@@ -128,8 +128,8 @@
     a measurable impact on performance, since the compiler is forced to load
     the page size from memory rather than embedding immediate values.
 
---disable-lazy-lock
-    Disable code that wraps pthread_create() to detect when an application
+--enable-lazy-lock
+    Enable code that wraps pthread_create() to detect when an application
     switches from single-threaded to multi-threaded mode, so that it can avoid
     mutex locking/unlocking operations while in single-threaded mode.  In
     practice, this feature usually has little impact on performance unless