DOI lost when importing bibtex

Hi Ron,

When importing a bibtex file, the DOI is lost, using current CVS HEAD.

Here is an example file:

@Article{LANG-08a,
author = {Langer, M. and Cloetens, P. and Guigay, J. P. and Peyrin, F.},
title = {Quantitative comparison of direct phase retrieval algorithms in in-line phase tomography},
journal = {Medical Physics},
volume = {35},
pages = {4556-4566},
year = {2008},
doi = {10.1118/1.2975224},
keywords = {st2i, imagerie_volumique}
}