[metapost] Where is mfplain.mem supposed to be?

[Nicola]

Hi,
I am using Tex Live 2008 and I have successfully installed MetaPost 
1.201. Now, I need mfplain.mem (which, apparently, is missing from TeX 
Live), so I have created it with 'mpost -ini mfplain dump', which writes 
'mfplain.mem' into the current directory. I have tried to move the file 
into the same location as mpost.mem, but then mpost does not find it:

mpost '&mfplain' foo.mf

Sorry, I can't find that mem file; will try PLAIN.
I can't find the PLAIN mem file!

Should I put mfplain.mem somewhere else? Or should I update some other 
file in the distribution?

Nicola