Allow installing files named the same in different directories

This rewrites kdoctools_create_handbook and kdoctools_create_manpage so that
they work in situations like these:

    kdoctools_create_handbook(po/fr/index.docbook)
    kdoctools_create_handbook(po/es/index.docbook)

Which is what happens when they are called from kdoctools_install().

REVIEW: 118004