Fix build failure caused by Cython postprocessor

By far, Cython generates header in generated C source files like:

    /* Generated by Cython 0.19.2 on Thu Nov  7 18:09:16 2013 */

In some late versions of Cython (I tested on 0.21.1), The header's like:

    /* Generated by Cython 0.21.1 */

Current postprocessor presumes the header always containing build date, causing compiler error by producing unnecessary */ in the comment block if the header's not split properly.

This change resolves the bug by checking whether there's a build date in header and not appending extra */ if there's no build date in the header.