[Libreoffice] new module 'tail_build': a pseudo module to wrap build's tail-end gbuild-converted modules

This module exist only to take advantage of the ability of gbuild to build
multiple modules in one single Makefile.

A few module that normally get built at the end of the build process
are already converted. this 'pseudo-module' build them all as one.

As module get converted to gbuild they can be added to this module
if they fix the necessary pre-requisite. that is:

To qualify a module must not be the dependent of any other module,
except postprocess or if the other module itself is under tail_build

To migrate a module <foo> under tail_build, one should:

Merge the dependencies declared in <foo>/prj/build.lst into
tail_build/prj/build.lst
Remove the module <foo> from postprocess/prj/build.lst dependencies

Add the module name in Module_tail_build.mk at the root of bootstrap


at this point :
    chart2 \
    cui \
    dbaccess \
    formula \
    sc \
    sd \
    slideshow \
    starmath \
    sw \
    writerfilter

are combined in tail_build

looking at kohei's nice graph:
http://kohei.us/wp-content/uploads/2010/07/ooo-modules.png

'scripting' is bloking the inclusion of vbahelper (alredy gbuildified)

'desktop', 'extension' seems nice target for gbuildification...

'binfitler' will quickly get in the way... we will need to either
gbuildify it, or accept the penalty of having it build last (after
everything else)
the former is quite a lot of work, the later is easy: just add
tail_build as its dependency. Actually since binfilter is pretty big
and has a lot of sub-modules
it is quite likely the the over build time won't be much impacted...
as it use resource quite fully on it's own.

I tested things on Mac. it should be pretty platform-independent...

Norbert