coroapi.h: change lib_handler_fn's *msg to be const

Make a tiny type change and watch it propagate.

• include/corosync/engine/coroapi.h

(struct corosync_lib_handler) [lib_handler_fn]: Change type
of 2nd parameter: s/void *msg/const void *msg/.
Propagate the above into cfg.c and votequorum.c:

• services/cfg.c (message_handler_req_lib_cfg_get_node_addrs):

Constification exposed a bug in this function whereby it mistakenly
modified storage through its now-const *msg parameter. Since it
did that solely to store a temporary result, we've changed it
to use a local variable instead.

• services/votequorum.c (message_handler_req_lib_votequorum_setvotes):

Likewise.

• exec/vsf_quorum.c: add const to msg param.
• services/evs.c: Likewise.
• services/pload.c: Likewise.
• services/cpg.c: Likewise.
• services/confdb.c: Likewise.
• exec/coroipcs.h: signature of coroipcs_handler_fn_lvalue must match

that of lib_handler_fn; noted via main.c.

git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@2047 fd59a12c-fef9-0310-b244-a6a79926bd2f