Change interface to VG_(demangle) and VG_(maybe_Z_demangle)
to return a pointer to the untruncated demangled name. 
This change is identical to attachment 88001 of BZ 337869.


git-svn-id: svn://svn.valgrind.org/valgrind/branches/BUF_REMOVAL@14202 a5019735-40e9-0310-863c-91ae7b9d1cf9