Fix a use-after-free in unit tests. CID 752027
Fix a dead-code warning in unit tests. CID 1193548
Fix a c90 warning
Use evutil_weakrand() in unit tests.

(Coverity doesn't like random() or rand().  We don't care; this is
for unit tests.)

Fixes CID 1239298, 1239296, 1239295, 1239293.
Use a more precise calculation for max in time-ratelim.c

CID 1239297
Make a buffer larger in the tests to avoid a scary evbuffer_copyout_from()

The call was safe, but coverity couldn't tell. CID 1239294.
Fix for a677b72bd6d9d378daf9775966aa8ca574e26e67