make nat_cancel_sums simprocs robust in the presence of schematic variables; add regression tests
syntax: glob
*~
*.class
*.jar
.DS_Store
syntax: regexp
^contrib
^heaps/
^browser_info/
^doc-src/.*\.aux
^doc-src/.*\.bbl
^doc-src/.*\.blg
^doc-src/.*\.dvi
^doc-src/.*\.idx
^doc-src/.*\.ind
^doc-src/.*\.lof
^doc-src/.*\.log
^doc-src/.*\.out
^doc-src/.*\.toc
^src/Tools/jEdit/dist/