\fromafm always regenerates mtx file

[Alan Jeffrey]

Not really got much to say about \fromafm... I don't think there's a great
reason for not checking for the existance of the .mtx file, but...

> i could understand why extra spaces were added to the Asmall,
> but i could not understand why extra spaces were added to A.

An aesthetic decision on my part: I found that c&sc with sidebearings round
the sc but not the uc looked really uneven.  So I included sidebearings on
the uc as well.

Alan.