Lack of this feature resulted in the generation of incorrect *.pyf
files.

For example, the pyf file created by:

      subroutine sub3 (some arguments)
      real a, b, c, d
      common /coeff/ a, b
      common /coeff/ c, d

      <do stuff>

      return
      end

Should contain both common statements the declaration of all four
variables a, b, c, and d.

Closes #5876.

Also fix example in testing that Sphinx saw as section header.