[prop250] Pointer corruption and other failures in master and maint-0.2.8

Between 2da27186..7fa11a92 on master, and 01e7f42a..55cf1970 on maint-0.2.8, we merged code that causes crashes and make-test-network-all failures.

The following master make test-network-all tests fail on Linux:

FAIL: bridges-min
FAIL: hs-min
FAIL: bridges+hs

The following master make test-network-all tests fail on OS X:

FAIL: bridges-min
FAIL: hs-min
FAIL: bridges+hs
FAIL: bridges+ipv6-min
FAIL: ipv6-exit-min
FAIL: mixed

The following maint-0.2.8 make test-network-all tests fail on OS X:

FAIL: basic-min
FAIL: bridges-min
FAIL: hs-min
FAIL: bridges+hs
FAIL: bridges+ipv6-min
FAIL: ipv6-exit-min
FAIL: mixed

mixed uses 0.2.7.6 on my OS X.

The master OS X failures happen due to the following crash:

Application Specific Information:
crashed on child side of fork pre-exec
*** error for object 0x7fb203c032c0: pointer being freed was not allocated
 

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib        	0x00007fff9d1a6f06 __pthread_kill + 10
1   libsystem_pthread.dylib       	0x00007fff8daa84ec pthread_kill + 90
2   libsystem_c.dylib             	0x00007fff903bb6e7 abort + 129
3   libsystem_malloc.dylib        	0x00007fff8b468041 free + 425
4   tor                           	0x00000001060086b1 config_free_all + 321 (config.c:841)
5   tor                           	0x000000010606e233 tor_free_all + 179 (main.c:3170)
6   tor                           	0x000000010606e479 tor_cleanup + 313 (main.c:3239)
7   tor                           	0x0000000106067c31 consider_hibernation + 129 (hibernate.c:971)
8   tor                           	0x000000010606c7ce second_elapsed_callback + 590 (main.c:1467)
9   libevent-2.0.5.dylib          	0x0000000106261aa2 event_base_loop + 1871
10  tor                           	0x000000010606c245 do_main_loop + 1525 (main.c:2560)
11  tor                           	0x000000010606e586 tor_main + 230 (main.c:3660)
12  tor                           	0x0000000105fd8ce9 main + 25 (tor_main.c:30)
13  libdyld.dylib                 	0x00007fff982e35ad start + 1