fixes issue 1055 + initialize set_libc to NULL
fixes issue 1055
+ initialize set_libc to NULL

git-svn-id: fe3cd4388a6e5a968b09397a3d721fe124e8117a@1069 5b54908e-ead4-fc18-b48a-0285e6dbc711

rnk/drmemory,rnk/drmemory,rnk/drmemory,rnk/drmemory