Combination of 12 commits from interrupt_abort branch.

Basic strategy is to introduce bits to errflag and to set and
reset them separately.

Remove interrupt status on return to main keymap.

Turn off ERRFLAG_INT for always block.

Restore bit thereafter: we probably need a new variable in order
to allow user interrupts to be reset in the always block.

Add TRY_BLOCK_INTERRUPT

This works the same as TRY_BLOCK_ERROR, but for a SIGINT, too.

Ensure propagation of SIGINT from exited job.

If received by foreground job, shell uses ERRFLAG_INT, not
ERRFLAG_ERROR, to set the new state.

Reset errflag before precmd()

Add always block in _main_completion to fix ZLS_COLORS

Ensures we get the right state of $ZLS_COLORS at the end of _main_complete
even if there's an interrupt.  However, the "right state" is a bit messy
as it depends on styles.