[metapost] typos in mpman

[Stephan Hennig]

Hi Laurent,

Laurent Méhats schrieb:

> I've noticed two typos in the manual (the second one could be misleading).
> - p. 21, last sentence of sub-section 7.1,
>   "It conventional to use [...]": a "is" is missing.

And there was another period missing before "Thus" in the same paragraph.

> - p. 63, second sentence of the penultimate paragraph,
>   "[...] in place of a step b upto c.":
>   "upto" should be replaced with "until".

I have checked-in fixes (r1120, r1121).  Thanks!

Best regards,
Stephan Hennig