restore_term_settings: add warning message about SIGWINCH and Apache

This patch adds a warning in restore_term_settings() for
users testing DMTCP with Apache. Users should disable
the SIGWINCH that DMTCP sends on restart because Apache
uses that as a signal for terminating gracefully.

Future patches can include a method to do this automatically
by wrapping the call to send SIGWINCH in an ifdef that gets
disabled with a configure option.
exit wrapper: add comment about tgkill(SIGUSR2)

This patch adds a comment in the DMTCP exit wrapper in
miscwrappers.cpp about the tgkill(SIGUSR2) that is sent to
the ckpt thread when a user application thread under DMTCP
calls exit().
Merge branch 'apache-bbn' of https://github.com/dmtcp/dmtcp into apache-bbn

Conflicts:
	src/terminal.cpp