bibzbladd (and ma be others) strip @preamble from files

[pauloney]

A simple file like:

@preamble{
   "\def\cprime{$'$} "
}
@article {Sni,
    AUTHOR = {{\v{S}}nirel{\cprime}man, A. I.},
     TITLE = {Ergodic properties of eigenfunctions},
   JOURNAL = {Uspehi Mat. Nauk},
  FJOURNAL = {Akademiya Nauk SSSR i Moskovskoe Matematicheskoe Obshchestvo.
              Uspekhi Matematicheskikh Nauk},
    VOLUME = {29},
      YEAR = {1974},
    NUMBER = {6(180)},
     PAGES = {181--182},
      ISSN = {0042-1316},
   MRCLASS = {58G99 (35P20)},
  MRNUMBER = {0402834},
MRREVIEWER = {D. Newton},
}

recevies the ZBL number but gets the @Preamble strip off, making the bibtex file non-functional.