Added two different polling algorithms, a dumb one from VNC4, and an

Added two different polling algorithms, a dumb one from VNC4, and an
improved method which limits the rate of updates for continuously
changed areas such as video windows. Now there are three polling
algorithms supported, and the default is to use the new improved one.
New -PollingType options was added, it allows to select one of three
polling algorithms (0 - dumb, 1 - old, 2 - new).

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@340 3789f03b-4d11-0410-bbf8-ca57d06f2519