Removed --enable-allocator.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2772 ba6dc0ae-232f-0410-883f-9ebac64fc565
Added --enable-realtime-ckpt-signal configure flag

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2773 ba6dc0ae-232f-0410-883f-9ebac64fc565