SERVER-4328 if a lock is potentially nestable, like the local db lock…

…, do it after the "top lock"

otherwise, we could deadlock. this however means we can't commitIfNeeded on that database. the
claim is that that will be ok.

src/mongo/db/d_concurrency.cpp

@@ -565,12 +565,12 @@ namespace mongo {
         if (DB_LEVEL_LOCKING_ENABLED) {
             char db[MaxDatabaseNameLen];
             nsToDatabase(ns.data(), db);
-            if( str::equals(db,"local") ) {
-                lockLocal();
-            } else { 
+            bool loc = str::equals(db,"local");
+            if( !loc )
                 lock(db);
-            }
             lockTop(ls);
+            if( loc )
+                lockLocal();
         } else {
             lock_W();
             locked_w = true;
@@ -584,12 +584,12 @@ namespace mongo {
         if (DB_LEVEL_LOCKING_ENABLED) {
             char db[MaxDatabaseNameLen];
             nsToDatabase(ns.data(), db);
-            if( str::equals(db,"local") ) {
-                lockLocal();
-            } else { 
+            bool loc = str::equals(db,"local");
+            if( !loc )
                 lock(db);
-            }
             lockTop(ls);
+            if( loc )
+                lockLocal();
         } else {
             lock_R();
             locked_r = true;