makeinfo --docbook should include a newline in @docbook

[Aharon Robbins]

Hi.

Current makeinfo when processing @docbook ... @end docbook leaves off
the trailing newline. For example:

        @docbook
        <emphasis>&sim; Cn<superscript>2</superscript></emphasis>&thinsp;
        @end docbook
        peformance, while

This is wrong.  I have to add the &thinsp; at the end so that the result
doesn't run together with the following line:

        <emphasis>&sim; 
Cn<superscript>2</superscript></emphasis>&thinsp;performance, while

Much thanks,

Arnold