Clean up Sametime

[clokep]

While re-adding Sametime support to Instantbird I made Sametime compile with MSVC, Florian informed me that his changes of this type were accepted upstream.

This patch also adds in the Username Split that was removed at some point (I believe this was removed when the sametime plug-in was still part of a separate project on sourceforge).

I'm not sure how applicable it is, but our bug on the issue is: https://bugzilla.instantbird.org/show_bug.cgi?id=102

We have had reports that these changes work fine, although I'm not sure how backward compatible they are. I'm willing to put some effort into getting this upstream into libpurple, so let me know if things need to be changed.

[clokep]

MSVC compatibility & usernamesplit

[rekkanoryo]

I apologize for this patch sitting around for so long. Currently we have no one who is active in our development who knows anything about Sametime. That said, it compiles, so I'm shipping it.

[Patrick Cloke]

(In [0b7caf6b17815fe333d151369f26330d4c662bda]):
Fix up the Sametime prpl to play nice with Visual C++. This patch also puts back a username split that was removed just about forever ago. Fixes #14608.