More robust interrupt signalling

[shikokuchuo]

Vis. r-lib/mirai#240.

Tracking this at nanonext as the system-dependent behaviour points to a lower-level issue. Specifically interrupt handling is done differently by R on Windows / POSIX systems.

• Post Fix for POSIX platforms
• Merge Fix (if PR checks fine)
• Confirm Fix
• Revamp Tests
• Add news item

[shikokuchuo]

Also applies if tools::SIGINT is supplied to the autoexit argument of daemon().