cairo-gobject: require rcairo
gdk3: require rcairo
gtk2: require rcairo
gtk3: require rcairo
gtksourceview3: require rcairo
gtksourceview2: require rcairo
poppler: require rcairo
rsvg2: require rcairo
poppler: fix typo
poppler: remove needless "#if"

Because poppler-glib requires cairo support.
Update LGPL 2.1 files

GitHub: fixes #196

Reported by ktdreyer. Thanks!!!
gdk3 rbgdkwindow.c:  suppress deprecation warnings
gdk3 rbgdkdisplay.c: suppress deprecation warnings
gdk3: remove trailing spaces
fix build error

error: ‘mask’ undeclared (first use in this function)
add _DEVICE macro

Because we have to treat GdkDevice* type.
suppress incompatible pointer type warning
gdk3 rbgdkwindow.c: remove trailing spaces
gdk3: fix code style
gdk3: fix style

"Type *variable" is our style not "Type* variable".