Pidgin 2.7.6

# General:
- Included Microsoft Internet Authority 2010 and Microsoft Secure Server Authority 2010 intermediate CA certificates to our bundle. This fixes the "Unable to validate certificate" error for omega.contacts.msn.com.

# Pidgin:
- Avoid a use-after-free race condition in the media code (when there's an error reported by GStreamer).

# AIM and ICQ:
- SSL option has been changed to a tri-state menu with choices for "Don't Use Encryption", "Use Encryption if Available", and "Require Encryption".
- Fix some possible clientLogin URL issues introduced in version 2.7.5.
- Don't show a "<URL>: Ok" connection error when using clientLogin.
- Cleaned up some debug output for improved readability.

# MSN:
- Added support for MSNP16, including Multiple Points of Presence (MPOP) which allows multiple simultaneous sign-ins.
- Added extended capabilities support (none implemented).
- Merged the work done on the Google SoC (major rewrite of SLP code)
- Reworked the data transfer architecture. (SlpArchitecture)
- Lots of little changes.
- Don't process zero-length DC messages.
- Fixed a bunch of memory leaks.
- Prevent a use-after-free condition.

# XMPP:
- Avoid a double-free in the Google Relay (V/V) code.
- Avoid double error message when failing a file transfer.
- Password-related information is printed out for SASL authentication when the PURPLE_UNSAFE_DEBUG environment variable is set.
- Authentication mechanisms can now be added by UI's or other plugins with some work. This is outside the API/ABI rules!
- Fixed a few printf("%s", NULL) crashes for broken OSes.

# Windows-Specific Changes:
- Build the Pidgin Theme Editor plugin (finally).
- Untarring (for themes) now works for non-ASCII destination paths.