Fix build on older compilers that do not support 'd' suffix.

Things like:  if (foo > 0.0d) { }
fails to compile on Fedora 13 (at least) because the compiler
does not support a 'd' suffix properly.

Use a slightly uglier explicit cast to double to work around
this compiler limitation.

Signed-off-by: Ben Greear <greearb@candelatech.com>