Fixes include file issues for FreeBSD

MSWINDOWS was defined, even though I was working on the FreeBSD platform.
Suggestion would also be to remove LINUX defines, and use UNIX instead.
Fixes issue of GetCurrentThreadID return type

The TThreadID vs QWord type issue. I have used this work-around in many
projects, and it works well under FreeBSD, Linux and Windows. I can't
test under MacOSX, sorry.
Merge pull request #2 from graemeg/freebsd-fixes

FreeBSD fixes