Log Message:
Update to 4.1.0.

21 Oct 2014:
- Release 4.1.0
- Modernized autoconf build system
- Use constant-time comparisons where needed
- Use gcrypt secure memory allocation
- Correctly reject attempts to fragment a message into too many pieces
- Fix a missing opdata when sending message fragments
- Don't lose the first user message when REQUIRE_ENCRYPTION is set
- Fix some memory leaks
- Correctly check for children contexts' state when forgetting a context
- API Changes:
  - Added API functions otrl_context_find_recent_instance and
    otrl_context_find_recent_secure_instance.