Add a mutex on database access
API with direct cache access is deprecated

+fix memory leaks in tests

gcc was right to complain!

+ improve code readability

- this function shall be used in a mono-device per account environment
- give the trust status of a peer uri based on the
last device involved in a ZRTP exchange associated to that uri.

+ do not store in cache any peer information until first negotiation succeeds

- Stick to old export key only when peer is BZRTP v1.0.x
- message to calling lib when peer is unlikely to implement LIME

- allow passing also a string
- add peer version obsolete message
+ add cache mismatch information in the secrets structure

- add binding ZID/sipURI in cache to prevent evil friend attack
- expose read/write cache API for external use(LIME)
- add callback to give information to user(cache mismatch only for now)
- stick to RFC 4.5.2 for exported key generation
  (but use the ZRTP Client ID to ensure backward compatibility)
- direct access to exported key computation(not anymore related to cache)
- add cache related tests

Note: no cache migration function provided

. flag to enable or not multiple tag with the same name under <peer> node

+ remove useless isSecure function

+add a get channel status function

before DHM on first one complete.

Signed-off-by: Johan Pascal <johan.pascal@belledonne-communications.com>

- loadCache should not assume the buffer is allocated with malloc. Instead, a function to call for freeing the buffer is to be passed.
- replace setCallback() by setCallbacks() so that strong type checking is performed on the supplied callbacks.