Fixes 282230 group allocator for small fixed size, use it for MC_Chunk/SEc vbit

Fixes 282230  group allocator for small fixed size, use it for MC_Chunk/SEc vbit

* new files include/pub_tool_groupalloc.h and coregrind/m_groupalloc.c
  implementing a group allocator (based on helgrind group alloc).
* include/Makefile.am coregrind/Makefile.am : added pub_tool_groupalloc.h
  and m_groupalloc.c
* helgrind/libhb_core.c : use pub_tool_groupalloc.h/m_groupalloc.c
  instead  of the local implementation.
* include/pub_tool_oset.h coregrind/m_oset.c : new function
  allowing to create an oset that will use a pool allocator.
  new function allowing to clone an oset (so as to share the pool alloc)
* memcheck/tests/unit_oset.c drd/tests/unit_bitmap.c : modified
  so that it compiles with the new m_oset.c
* memcheck/mc_main.c : use group alloc for MC_Chunk
  memcheck/mc_include.h : declare the MC_Chunk group alloc
* memcheck/mc_main.c : use group alloc for the nodes of the secVBitTable OSet
* include/pub_tool_hashtable.h coregrind/m_hashtable.c : pass the free node
  function in the VG_(HT_destruct).
  (needed as the hashtable user can allocate a node with its own alloc,
  the hash table destroy must be able to free the nodes with the user
  own free).
* coregrind/m_gdbserver/m_gdbserver.c : pass free function to VG_(HT_destruct)
* memcheck/mc_replace_strmem.c memcheck/mc_machine.c
  memcheck/mc_malloc_wrappers.c memcheck/mc_leakcheck.c
  memcheck/mc_errors.c memcheck/mc_translate.c : new include needed
  due to group alloc.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12341