SSL/secure socket abstraction and SIP TLS transport rewrite

[nanang]

Objective:

To create a portable SSL/secure socket abstraction in PJLIB and to rewrite the SIP TLS transport in PJSIP.

Specifications:

1. General:
   • supports client and server socket operations (note: Symbian's CSecureSocket only supports client sockets)
2. I/O:
   • asynchronous I/O API similar to PJLIB's ​Active Socket API
   • timeout setting for SSL negotiation
   • buffer size control
3. Options:
   • select SSL version to use (SSLv23, TLSv1, etc)
   • select ciphersuite to use
   • verify server's certificate (note: not available on Symbian)
   • verify client's certificate (note: not available on Symbian)
   • TLS server name extension to support connecting to multihosted TLS server (note: only available on recent OpenSSL versoins)
4. Certificate management (note: not available on Symbian):
   • specify which certificate to use
   • load the certificate, either from file(s) or OS's certificate store.
   • retrieve certificate infos.

Backends:

1. OpenSSL
2. CSecureSocket on Symbian

[nanang]

In r2913, initial version of TLS transport for Symbian, includes:

• Secure socket, generic abstraction and Symbian implementation (using CSecureSocket).
• Initial rewrite of SIP TLS transport.
• Updated symbian_ua.mmp to support SIP transport TLS (experimental).

[nanang]

In r2950:

• Added SSL socket abstraction with OpenSSL backend (source only, i.e: hasn't been integrated to build settings).
• Updated cipher data type and added cipher constants (Symbian SSL socket has also been updated).
• Updated SIP TLS transport to allow setting certificate/credential (via file).