Ported encoding optimizations from TurboVNC. The changes to the Tight parameters...

Ported encoding optimizations from TurboVNC.  The changes to the Tight parameters were determined through extensive low-level profiling (see http://www.virtualgl.org/pmwiki/uploads/About/turbototiger.pdf).  The other enhancements involved: (1) porting the solid subrectangle pre-computation code from TightVNC/TurboVNC (it makes a pretty big difference-- see report), (2) encapsulating the JPEG encoder in its own class (this eliminates a buffer copy, and the JPEG buffer is now set to a decent size where it shouldn't ever need to be paged or re-allocated, except in rare corner cases), (3) adding support for last rect. encoding (necessary to support the solid rectangle pre-computation enhancements.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4626 3789f03b-4d11-0410-bbf8-ca57d06f2519