problems with c-fill-paragraph, c++ comments in c modules

[Ragweed <jeffrey.magill@gmail.com>]

I've recently built Emacs 23.2.1 on a linux box and it doesn't behave
the same as the Emacs 21.4.1 on the same host with respect to c++
comments in a c file.  I can't figure out how to get Emacs 23.2.1 to
run c-fill-paragraph properly for c++-style comments when they're in a
c file.

Consider the following long c++ style comment in a file named test.c:
>// The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.

If I run c-fill-paragraph with the cursor  on that line, Emacs 21.4.1
converts it to what I want:
>// The quick brown fox jumps over the lazy dog. The quick brown fox jumps over
>// the lazy dog. The quick brown fox jumps over the lazy dog.

If I run c-fill-paragraph in 23.2.1, I get:
// The quick brown fox jumps over the lazy dog. The quick brown fox
jumps over
the lazy dog. The quick brown fox jumps over the lazy dog.

That is, it wraps the comment to the next line but doesn't prefix the
next line with the comment prefix.

If I rename the file to test.cpp, then emacs 23.2.1 DOES prefix the
line.

I renamed my .emacs file so that both versions of Emacs use their
default settings and ignore my normal customizations.