[External Deps] Updated recommended popper version to 0.6.3

[Luca Ferretti <elle uca libero it>]

I've just updated jhbuild moduleset and wiki page for 2.22. 

I'll update garnone in the next days (or at least I'll open a bug)

Changes between 0.6 and 0.6.3 can be found here (a lot of fix, no new
stuff):
http://lists.freedesktop.org/archives/poppler/2007-October/002995.html
http://lists.freedesktop.org/archives/poppler/2007-November/003136.html
http://lists.freedesktop.org/archives/poppler/2007-December/003207.html


PS should we add poppler-data to jhbuild build and in ext deps list?
>From poppler-data README:

        This package consists of encoding files for use with poppler.
        The encoding files are optional and poppler will automatically
        read them
        if they are present.  When installed, the encoding files enables
        poppler to correctly render CJK and Cyrrilic properly.  While
        poppler is licensed under the GPL, these encoding files are
        copyright Adobe and licensed much more strictly, and thus
        distributed separately.