[ptx] Panotools check in m4

[Edouard Gomez]

The Panotools check is not flexible enough to cope with non
standard lib/include dirs.

With gcc, CPATH can be used to specify aditional locations ofr
include dirs, and LIBRARY_PATH does the same for libs to link
against.

They follow the usual dir1:dir2:dir3 format, playing with the
IFS variable should be enough to split the CPATH and
LIBRARY_PATH vars and include them in the panotools check.

-- 
Edouard Gomez