Cactus's include mechanism creates empty files for jconfig.h and jpeglib.h in configs/<configname>/bindings/include since no thorn actually provides these include files (in particular ExternalLibraries/libjpeg does not). Instead these files are regular include files like hdf5.h so no special mechanism to include them is required.
Right now the "USE include header" statements in interface.ccl prevent IOJpeg from finding the include files in /usr/include (which appears later in the include search path I assume).
Ok, to be applied? Since this thorn lives in Cactuscode I cannot apply the patch myself.