bugfix.  lcm_udp don't try to allocate space from ringbuffer until select() indicates that new incoming data is ready.  this also eliminates an infinite loop that occurs in lcm_destroy() when an lcm_t with a full ringbuffer is destroyed (recv_thread never terminates because of neverending attempt to allocate from ringbuffer).
bugfix.  lcm_udp don't try to allocate space from ringbuffer until select()
indicates that new incoming data is ready.  this also eliminates an infinite
loop that occurs in lcm_destroy() when an lcm_t with a full ringbuffer is
destroyed (recv_thread never terminates because of neverending attempt to
allocate from ringbuffer).


git-svn-id: ddc8cd1199829c18fa5932f18135ba8f687fc5aa@236 989093bb-e83e-0410-a25a-9184cbcad8d0

tprk77/lcm-tprk77,tprk77/lcm-tprk77,tprk77/lcm-tprk77,tprk77/lcm-tprk77,tprk77/lcm-tprk77,tprk77/lcm-tprk77,tprk77/lcm-tprk77