use Exn_printer-based exception handling everywhere

TODO

src/core/env.mli

src/driver/driver_lexer.mll

src/driver/whyconf.ml

src/driver/whyconf.mli

src/ide/gmain.ml

src/manager/db.ml

src/manager/gmanager.ml

src/manager/test.ml

src/parser/denv.ml

src/parser/denv.mli

src/parser/lexer.mli

src/parser/lexer.mll

src/parser/typing.ml

src/parser/typing.mli

src/programs/pgm_lexer.mll

src/programs/pgm_main.ml

src/programs/pgm_typing.ml

src/programs/pgm_typing.mli

src/tptp2why/tptp2why.ml