rb_uninterruptible() disables any interrupts using handle_interrupt
feature (This function is used by `p`).
After this function, pending interrupts should be checked correctly,
however there is no chance to setup interrupt flag of working
threads, it means that nobody checks pending interrupts.
For example, it ignores terminate signal delivered at the end
of main thread and program can't stop.

This patch set interrupt flag if there are pending interrupts.