This patch adds cgroup_create_cgroup_from_parent() API. I've tested it

This patch adds cgroup_create_cgroup_from_parent() API. I've tested it
with a modified version of libcg_ba (basic acceptance tests), that I'll send
out later. I've also fixed a couple of bugs, I'll list them in order and
if desired, I'll split out the patches so that the enhancements can be
separate from the bug fixes

1. Fix cg_create_control_group() to succeed if the directory already exists
2. We can't always append a control_file, we need to open it "r+"
3. It's OK for writing values to a  control_file to fail, since some of
   them are read-only and some may not exist in hierarchies below the root
4. Skip over directories while trying to read control file's name value pairs
5. In cg_rd_ctlr_file we don't allocate any memory to value, directly fscanf
   into it, that's been fixed
6. There might be more fixes that might already be present in trunk, since
   I hope I've not redone a lot of the fixes, I had branched of trunk very
   recently

Changelog v2
------------
1. Refactor cgroup_free_controllers() and use it in
        cgroup_create_cgroup_from_parent()
2. Check for strdup failure
3. Check if dst == src

TODO:

1. Use cg_add_controller() API
2. Use cg_add_value_string() API

I'll send out patches for the TODOs later.

I've also updated the basic acceptance test (libcg_ba.cpp)

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
git-svn-id: https://libcg.svn.sourceforge.net/svnroot/libcg/trunk@165 4f4bb910-9a46-0410-90c8-c897d4f1cd53