[pdftex] map files again

[The Thanh Han]

> since we are at the map file subject again: I feel the need for specifying
> additional map file via some commandline switch. That way, people could
> embed fonts (e.g. the base 14) which they normally don't embed.
> 
> A related issue is that it might really be helpful to load a second
> entry for a font  where the later loaded entry just overwrites the
> earlier one as in dvips.

yes this seems to be a better behaviour; at the moment pdftex ignores
later entries with the same tfm names.

Thanh