Вот все, что он проставляет во время "make install":
===============
dir /usr
dir /usr/local
dir /usr/local/lib
dir /usr/local/lib/gtk-2.0
dir /usr/local/lib/gtk-2.0/2.4.0
dir /usr/local/lib/gtk-2.0/2.4.0/engines
obj /usr/local/lib/gtk-2.0/2.4.0/engines/libcaligula.la
obj /usr/local/lib/gtk-2.0/2.4.0/engines/libcaligula.so
dir /usr/local/share
dir /usr/local/share/themes
dir /usr/local/share/themes/Caligula
dir /usr/local/share/themes/Caligula/gtk-2.0
obj /usr/local/share/themes/Caligula/gtk-2.0/gtkrc
dir /usr/local/share/themes/Caligula-grassy
dir /usr/local/share/themes/Caligula-grassy/gtk-2.0
obj /usr/local/share/themes/Caligula-grassy/gtk-2.0/gtkrc
dir /usr/local/share/themes/Caligula-sketchy
dir /usr/local/share/themes/Caligula-sketchy/gtk-2.0
obj /usr/local/share/themes/Caligula-sketchy/gtk-2.0/gtkrc
dir /usr/local/share/themes/Caligula-swirly
dir /usr/local/share/themes/Caligula-swirly/gtk-2.0
obj /usr/local/share/themes/Caligula-swirly/gtk-2.0/gtkrc
===============
И в проставляемых темах в качестве движка указан caligula. Вообще никаких намеков на cairo-gtk-engine :(