patch: make hexl mode support 8, 32 and 64 bit groups

[Vivek Dasmohapatra]

The hexl binary supports 8, 16, 32 and 64 bit groups, but hexl mode
currently only supports 16 bit groups.

This patch adds support (controlled by a custom item, `hexl-bits')
for the other group sizes.

Oh, and there was a minor bug in hexl-scroll-up (and -down) which meant it
scrolled by one line too many (didn't take account of the ruler line) by
default, so you;d miss one line of data if you weren't careful.

Change log entry included.

hexl.8-16-32-64.patch
Description: Text document