Bug#649905: blackbox: FTBFS: libbt0.symbols 64-bit specific

["Aaron M. Ucko" <ucko@debian.org>]

Source: blackbox
Version: 0.70.1-4
Severity: serious
Justification: fails to build from source (but built successfully in the past)

Per https://buildd.debian.org/status/package.php?p=blackbox, builds of
blackbox on 32-bit architectures have been failing because
libbt0.symbols only matches libbt.so.0's actual symbols on 64-bit
architectures (amd64, ia64, and kfreebsd-amd64).  Could you please
account for architecture-specific variation?

Thanks!