Allow only one instance of OpenCS.  Only tested on windows x64.
Use append syntax compatible with older versions of boost.
Merge remote-tracking branch 'remotes/upstream/master' into single-instance

Conflicts:
	apps/opencs/editor.cpp
Workaround file lock being lost if the same file is closed elsewhere in the program (see https://svn.boost.org/trac/boost/ticket/3582)