Allocate serf_ssl_context_t in bucket pool instead of global pool to fix  issues when apr_terminate() is called without clearing connection pool.
Allocate serf_ssl_context_t in bucket pool instead of global pool to fix 
issues when apr_terminate() is called without clearing connection pool.

See thread "Serf / SSL coredumps during apr_terminate" in serf-dev:
https://groups.google.com/d/msg/serf-dev/gOn9HTUN98U/pz0_AqdrmJYJ 

* buckets/ssl_buckets.c
  (ssl_init_context): Allocate serf_ssl_context_t in provided bucket 
   allocator instead of creating global pool.
  (ssl_free_context): Remove code to destroy global pool.
  (serf_bucket_ssl_create): Pass allocator to ssl_init_context() call.
alex1818/serf,stoneCC/serf,google-code-export/serf,google-code-export/serf,x-clone/serf,SirJson/serf,yesoce/serf,yesoce/serf,zhengcq315/serf,google-code-export/serf,lazysoez/serf,soufianeEL/serf,zhengcq315/serf,SirJson/serf,pengdu/serf,zhupan/serf,zhupan/serf,pengdu/serf,KyleSanderson/serf,alex1818/serf,soufianeEL/serf,alex1818/serf,google-code-export/serf,KyleSanderson/serf,x-clone/serf,alex1818/serf,yesoce/serf,yesoce/serf,soufianeEL/serf,lazysoez/serf,stoneCC/serf,pengdu/serf,zhengcq315/serf,zhengcq315/serf,KyleSanderson/serf,soufianeEL/serf,x-clone/serf,lazysoez/serf,SirJson/serf,SirJson/serf,lazysoez/serf,stoneCC/serf,stoneCC/serf,pengdu/serf,zhupan/serf,KyleSanderson/serf,zhupan/serf,x-clone/serf