Added a mutex lock in fillMeas to avoid segfaults when used in multiple threads


git-svn-id: http://casacore.googlecode.com/svn/trunk@21431 6afa274c-0927-0410-9b47-a1284d797885
Use ImageProxy to copy the image (expression).
Not only does it save code, but it also solves the problem of handling
a single image


git-svn-id: http://casacore.googlecode.com/svn/trunk@21432 6afa274c-0927-0410-9b47-a1284d797885