Factorise enum set parsing code
* add a function Bool VG_(parse_enum_set) in pub_tool_libcbase.h/m_libcbase.c
  (close to Bool VG_(parse_Addr)
* Implement Bool MC_(parse_leak_heuristics) and MC_(parse_leak_kinds)
  as a call to VG_(parse_enum_set)



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13898 a5019735-40e9-0310-863c-91ae7b9d1cf9
Reword/clarify the VG_(parse_enum_set) comment.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13899 a5019735-40e9-0310-863c-91ae7b9d1cf9