Emergency PR: Avoid breakage on emacs < 29.1

[dankessler]

A PR that I wrote was recently merged, but has caused problems for anyone using bind-map with emacs < 29.1.

The problem is in order to find aliased modes, I used function-alias-p, but this is only available in emacs 29.1+. As a result, anyone with emacs < 29.1 who is using the new version of emacs will get a cryptic error about Symbol's function definition is void: function-alias-p. My bad! :(

Handling aliased modes is important, because this is how AUCTeX remaps its modes in older versions of emacs (where major-mode-remap-alist is not available). However, while I/we try to add this functionality to bind-map, I wanted to fix my mistake and at least make bind-map work on older versions of emacs.

This PR just adds some logic to ensure that function-alias-p is available before trying to use it. If this looks cursorily good, I hope we can get it adopted ASAP so that it can make its way to MELPA.

[justbur]

Thank you

[dankessler]

Thanks for moving on this so quickly and sorry for the mistake!