more general command 'generate_file' for registered file types, notably Haskell;
discontinued 'generate_haskell_file', 'export_haskell_file';
eliminated generated sources: compile files in tmp dir;
src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools