vle: allow assign local to POSIX

By default, VLE use the locale according to the environment variables.
In library mode, a "POSIX" or "C" locale can be used. We add a new
constructor to to vle::Init class to permit "POSIX" locale.
vle: add WITH_COVERAGE option in CMake

We need to perform coverage test in VLE. So, we add the gcc `--coverage'
option in CFLAGS, CXXFLAGS and LDFLAGS if the user selects the
WITH_COVERAGE option in CMake.
value: remove boost::serialization depends

Since VLE 1.1 does not (de)serialize value between components, we can
remove this dependency to Boost.
template: assign default path for scripts

Assign a default path scripts Vle*.cmake since CMake complains to not
found these scripts.
utils: split source/binary package

We change the behaviour of packages in VLE. Now, the VLE_HOME directory
stores only the binary version of packages. The source code must be
anywhere on the system.

For example, the source package is in $HOME:
$ cd $HOME
$ vle -P foo create

The binary package goes to the $VLE_HOME/pkgs-1.1 directory:
$ vle -P foo configure build
$ ls $VLE_HOME/pkgs-1.1/foo
Authors.txt  Description.txt  exp          News.txt  plugins
data         doc              License.txt  output    Readme.txt
vle: allow building of VLE with old system

We allow to build VLE (but without Gvle) on old system i.e. with
libarchive 2.8.x and boost and boost asio <= 1.41
vpz: add missing iterator header

Add the iterator standard header. This file is missing in Views for some
compiler/architecture.
gvle: add the GlobalPlugin system

In order to customize deeply the gvle GUI, a GlobalPlugin class has
been added. It does allow to add widget to the GUI.
- Gvle has been enhanced to check fo each global plugin availabe and
  to run them.
- The PluginFactory has been changed in order to keep during all the
  session the already loaded plugin available, insteed of relaxing the
  ressources as soon as a plugin has been used once.
gvle: fix the bug of the Project menu

Due to a change of the spawn managment system, the Project menu was
available only once.  After the usage of a menu entry like Configure,
the menu was not available anymore. The way to use the package methods
has been changed in order to fix this bug.
cmake: remove chrono library if find_boost fails

We need to check if the chrono library is available. If it not, we need
to run find_boost twice without chrono.
all: update to gcc 4.4.6

We change source code in many files to use GCC 4.4.6.
vle: update README

Update the README file with newest dependency.
gvle: fix the plugin file generation

gvle assume that the folder loaded is a project working directory. It
does keep it as a member field. And when a plugin does want to save a
generated file, the expected place is the "src" subdirectory of the
project source directory (Closes #63,#62).