Fix duplicate definition of '_BP_PAINTPARAMS'

The header 'os.h' includes 'uxtheme.h' which defines '_BP_PAINTPARAMS'.
However, for some reason the #ifndef _BP_PAINTPARAMS directive in 'os.h'
does not work and a duplicate definition occurs. (GCC/2 v4.7.3)
Compiling against 'odin32-swt' r22079

Using 'odin32-swt' revision: "Fix nameless union in 'msctf.h'"
http://trac.netlabs.org/odin32/changeset/22079/branches/swt
Compiling against 'odin32-swt' r22080

Using 'odin32-swt' revision: "Added missing structures and callback types"
http://trac.netlabs.org/odin32/changeset/22080/branches/swt
Compiling against 'odin32-swt' r22081

Using 'odin32-swt' revision: "Modified or replaced some structures"
http://trac.netlabs.org/odin32/changeset/22081/branches/swt

All sources for swt.dll now compile.