Some of the usages of GetPos were just misusing it to find out
whether a vector contains given element -- use Contains() in those
cases

This patch is partially based on work of Christoph Lutz

Conflicts:
	sw/source/filter/ww8/wrtw8esh.cxx
	sw/source/filter/ww8/wrtw8num.cxx

Change-Id: I40bedba905e7577ba23f69acee178e0ea7cc1521