background thread not shutdown during session close

[gladish]

==9882==
==9882== HEAP SUMMARY:
==9882== in use at exit: 5,288 bytes in 6 blocks
==9882== total heap usage: 12 allocs, 6 frees, 12,032 bytes allocated
==9882==
==9882== 272 bytes in 1 blocks are possibly lost in loss record 2 of 5
==9882== at 0x4C31B25: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==9882== by 0x40134A6: allocate_dtv (dl-tls.c:286)
==9882== by 0x40134A6: _dl_allocate_tls (dl-tls.c:530)
==9882== by 0x544B227: allocate_stack (allocatestack.c:627)
==9882== by 0x544B227: pthread_create@@GLIBC_2.2.5 (pthread_create.c:644)
==9882== by 0x4E42348: lifxThread_Create (lifx.c:260)
==9882== by 0x4E4CAF8: lifxSession_Open (lifx_session.c:196)
==9882== by 0x108C87: main (async.c:50)
==9882==
==9882== LEAK SUMMARY:
==9882== definitely lost: 0 bytes in 0 blocks
==9882== indirectly lost: 0 bytes in 0 blocks
==9882== possibly lost: 272 bytes in 1 blocks
==9882== still reachable: 5,016 bytes in 5 blocks
==9882== suppressed: 0 bytes in 0 blocks
==9882== Reachable blocks (those to which a pointer was found) are not shown.
==9882== To see them, rerun with: --leak-check=full --show-leak-kinds=all