Add cscope generated files to .gitignore.

Closes #13092; patch from dgoulet.
Expand the event_mask field in controller conns to 64 bits

Back in 078d6bcd, we added an event number 0x20, but we didn't make
the event_mask field big enough to compensate.

Patch by "teor". Fixes 13085; bugfix on 0.2.5.1-alpha.
Merge branch 'maint-0.2.5' into release-0.2.5