even though exo-0.6.0 is installed, configure fails with the error message:

  # checking for optional package exo-0.3 >= 0.3.0... not found
  # checking for exo-0.2 >= 0.2.0... not found
  # *** The required package exo-0.2 was not found on your system.
  # *** Please install exo-0.2 (atleast version 0.2.0) or adjust
  # *** the PKG_CONFIG_PATH environment variable if you
  # *** installed the package in a nonstandard prefix so that
  # *** pkg-config is able to find it.

this appears to be because exo-0.6.0 actually installs exo-1.pc

  sedit 's/exo-0.3/exo-1/' configure

allows the configure script to complete successfully.