[Notion-devel] make automagic - first step to git submodules

[ebik <eb...@dr...>]

We rely on GNUMake anyway, thus I added some Make automagic, that
detects if libtu and/or libextl is copied into properly named
subdirectory of notion, and setups then accordingly (it behaves then
like makefiles in snapshot, i.e., the included libtu and libextl uses
system.mk and others of the parent directory (notion)). The main idea
is to pass a make variable SUBMODULE=1 to subdirectories, and let libtu
and libextl makefiles set TOPDIR to .. when they detect this variable.
The second part is autodetection in libs.mk, that uses libtu and
libextl from subdirectories of notion, if they are there.

I also added autodetection, if there is lua5.1 in pkg-config. If so,
then 'debian' way of lua setup is used, otherwise '/usr/local/...'
paths are used.

The branches are on standard location:
http://drak.ucw.cz/~ebik/git/notion
http://drak.ucw.cz/~ebik/git/libtu
http://drak.ucw.cz/~ebik/git/libextl

These patches are more or less needed, if we want to use git-submodule.
The second step is to setup the submodules properly, so that they will
be automatically checked in 'libtu' and 'libext' subdirectories, when
user types:
git submodule update --init
(after the initial clone, subsequent updates need not the --init option)

The nice thing on submodules is, that git knows (i.e., commiter must
tell) which versions(comits) of submodules belongs to particular commit
of project that includes these submodules. Here is the git
documentation: http://book.git-scm.com/5_submodules.html

-- 
                                 Tomáš 'ebík' Ebenlendr
                                 PF 2011.27951303272