Always run java with 5MB heap.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2240 ba6dc0ae-232f-0410-883f-9ebac64fc565
Unblock ckpt-signal on startup.

On some systems, the ckpt-signal may be blocked by default. We should
unblock it before proceeding further. This was observed on LIGO systems
with bash.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2241 ba6dc0ae-232f-0410-883f-9ebac64fc565