SERVER-13912 Better write intents for RSV1Base::deleteRecord

Only declare intent to write to areas we actually write to, rather than the
entire Extent header. Most of the time (ie unless deleting the first or last
record) no write intents should be declared.

src/mongo/db/structure/record_store_v1_base.cpp

@@ -287,14 +287,16 @@ namespace mongo {
 
         /* remove ourself from extent pointers */
         {
-            Extent *e = txn->recoveryUnit()->writing( _getExtent( _getExtentLocForRecord( dl ) ) );
+            Extent *e =  _getExtent( todelete->myExtentLoc(dl) );
             if ( e->firstRecord == dl ) {
+                txn->recoveryUnit()->writing(&e->firstRecord);
                 if ( todelete->nextOfs() == DiskLoc::NullOfs )
                     e->firstRecord.Null();
                 else
                     e->firstRecord.set(dl.a(), todelete->nextOfs() );
             }
             if ( e->lastRecord == dl ) {
+                txn->recoveryUnit()->writing(&e->lastRecord);
                 if ( todelete->prevOfs() == DiskLoc::NullOfs )
                     e->lastRecord.Null();
                 else