chapter heading: fix bad box due to parskipfill

[bennofs]

parskipfill causes spaces to be added after the end of the paragraph, resulting in a ugly badbox if parskip=half or parskip=full is used.

Before:

After:

[atifraza]

Thanks for the fix. Just applied and fixed all those Overfull warnings for chapter headings.

[atifraza]

PR 119 and this one modify settings for ctchapternumber.

Needs checking if other things don't get affected.