current canvas. This is useful to export dirty rectangles. Accordingly,
add caca_import_area_from_memory() and caca_import_area_from_file().

split is rendered moot by the plugin system: when enabled, binaries do
not link directly with libX11 or libGL. I hope this is a step towards
more consisteny and clarity.

accordingly.
  * The C++ test example no longer needs "config.h".

* Renamed canvas handle variables from "c" to "cv". Eh ouais mon gros.