Move MtcpRestartThreadArg struct to util.h

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2828 ba6dc0ae-232f-0410-883f-9ebac64fc565
Move threadinfo.c code into threadlist.cpp.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2829 ba6dc0ae-232f-0410-883f-9ebac64fc565
Mark ThreadList::postRestart as rst entry function.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2830 ba6dc0ae-232f-0410-883f-9ebac64fc565