Wrapping the jpeg support library for tcl is a bit more complicated
than libz, or libpng.

(1)	libjpeg comes with its own configure command, and there is no
	configure.in. This means that it is not possible to lift the
	relevant sections out of it for the configure of the
	binding. Instead the binding run the configure of libjpeg
	(AC_CONFIG_SUBDIRS) from its own configure and uses the
	resulting header file (jconfig.h) as usual. A quirk is that
	the tcl binding is a subdirectory of libjpeg, but to be able
	to perform the previous operation its has to be the other way
	around (AC_CONFIG_SUBDIRS is unable to handle '..'
	correctly). To facility this I placed a symbolic link into the
	directory of the binding, refering to the parent under the
	name libjpeg.

(2)	A second trouble spot is described in the file 'DANGER'.