shell-pop breaks list-registers

[wginolas]

Hi,

shell-pop uses a keyword symbol as register name (https://github.com/kyagi/shell-pop-el/blob/master/shell-pop.el#L308). This breaks list-register which tries to sort the registers by name.

sort: Wrong type argument: number-or-marker-p, :shell-pop

The docstring of register-alist states that only characters are allowed as register names.

[Shohei YOSHIDA]

I have sent PR about replacing using register implementation at #54.

[wginolas]

That was fast! Thank you very much!

[Shohei YOSHIDA]

Merged #54.