When handling client munmaps and mprotects with r=0 & w=0, actually

When handling client munmaps and mprotects with r=0 & w=0, actually
paint the relevant address range as NoAccess rather than ignoring the
event.  This is important for avoiding VTS leaks in libhb_core.
More details in comments in the code.

Also rename the _noaccess_ painters that do nothing to make it clearer
that they do nothing :-)

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11654