Bug fixes:

• Fix a race in the "arenas.extend" mallctl that could cause memory corruption of internal data structures and subsequent crashes.
• Fix Valgrind integration flaws that caused Valgrind warnings about reads of uninitialized memory in:
  • arena chunk headers
  • internal zero-initialized data structures (relevant to tcache and prof code)
• Preserve errno during the first allocation. A readlink(2) call during initialization fails unless /etc/malloc.conf exists, so errno was typically set during the first allocation prior to this fix.
• Fix compilation warnings reported by gcc 4.8.1.