Disable Composite extension by default in the legacy-friendly TigerVNC build. Justif...

Disable Composite extension by default in the legacy-friendly TigerVNC build.  Justification:  Some older versions of Gnome do not work properly when Composite is enabled.  This is known to be a problem with RHEL 4 (Gnome 2.8), and it causes the legacy-friendly build to be unusable on that platform.  Newer Gnome versions, such as 2.16.0 (the version in RHEL 5), work properly with Composite enabled, but those versions don't support compositing anyhow, so it doesn't matter if we remove the extension.  Typically, platforms that are new enough to support compositing are also new enough to not require the legacy-friendly build of TigerVNC.  Further, Composite can be re-enabled by simply adding --enable-composite to the XORGCFGFLAGS env. variable prior to executing 'build-xorg build'.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4686 3789f03b-4d11-0410-bbf8-ca57d06f2519