Docbuilding Howto updated

The Docbuilding Howto has been updated.

A warning and a workaround have been added regarding the problems that can occur if you check out the manual module into a path that contains spaces or other non-alphanumerical characters.

For a complete list of changes (this is especially important for translators)
see the Document History (Revision 1.6):

http://www.firebirdsql.org/manual/docbuildhowto-dochist.html