--enable-telepathy vs. GTK3

[Stephan Bergmann]

FYI, just noticed on Linux master (at least) that --enable-telepathy 
effectively disables the GTK3 VCL backend:  The LO sofficeapp lib links 
against the LO tubes lib, which links against GTK2 libs, so those libs 
are loaded by the time the vclplug_gtk3 lib tries to call (GTK3's) 
gtk_check_version (in create_SalInstance, vcl/unx/gtk3/gtk3gtkinst.cxx 
including vcl/unx/gtk/gtkinst.cxx), so it actually calls GTK2's 
gtk_check_version, which fails with a "gtk version conflict: Gtk+ 
version too old (major mismatch)" SAL_WARN.

Probably just another nail in (disabled-by-default) --enable-telepathy's 
coffin (unless somebody changes it to use GTK3, presumably).