Split header file III

Split header file III

Changelog:
 - since there are no global macros, base.h is gone
 - since there is no base.h, all headers need to include <features.h> to get
   __BEGIN_DECLS
 - new init.h with cgroup_init() and cgroup_get_subsys_mount_point()
 - new error.h with error handling enum and related stuff
 - use #ifndef _LIBCGROUP_*_H instead _LIBCG_*_H in header guards
 - fix few checkpatch complaints (long lines, whitespaces, ...)

The patch includes Makefile and .spec changes. I tested it compiles,
make dist produces tarball with all headers, so does also the rpm.
'make' should automatically catch all changes in new headers and
recompile dependent (=all) sources when any header changes.

libcgroup.h
  - does not declare anything, it just includes all the other files. In
    future, it might contain base of doxygen documentation (some
    introduction etc.)

libcgroup/error.h
  - the big enum with errors + error related functions

libcgroup/init.h
  - libcgroup_init() and cgroup_get_subsys_mount_point()

libcgroup/config.h
  - configuration reading/unloading

libcgroup/groups.h
  - group manipulation stuff (create/modify/delete/free, incl. controllers and
    get/set values) + definition of struct cgroup (=must be included by
    libcgroup/tasks.h, which needs it)

libcgroup/iterators.h
  - various walks, *_begin/next/end

libcgroup/tasks.h
  - task classification, incl. rules cache manipulation

In addition, I probably removed some #includes, which are not needed now when
looking for the minimal #include set to build the project. I also hope I did not
miss any function declaration or macro...

Signed-off-by: Jan Safranek <jsafrane@redhat.com>
Signed-off-by: Dhaval Giani <dhaval.giani@gmail.com>