pjsip: Fix COM multithreading issues in DirectShow backend

Ignore-this: a61d22db7faf7f22e59e8285191c0aaf

When using Qt, COM is initialized with COINIT_APARTMENTTHREADED, so we cannot
initialize it with COINIT_MULTITHREADED. Also, using COINIT_MULTITHREADED is not
an option because Qt initializes it via OLE, which is not thread safe, and if
OLE is not initialized some functionality such as drag & drop is lost.

darcs-hash:20140812105103-56b4d-348866aa72c89a8b80af83459f7732aa60719d6d
pjsip: Use UTF-8 encoding for video device names on OSX

Ignore-this: 39d847b3473a3ec8df950438e554a8d3

darcs-hash:20140818143446-56b4d-b0cd4628d9a639ef812bed34778a107186648ae4
pjsip: use default format if none was detected on OSX video backend

Ignore-this: 19cd5d5225dc4a843b94321d1ca68b45

darcs-hash:20140818143633-56b4d-9d6967e888c506c1741bf089cfce84b4e05dd6bc