[e-acsl] possible to customize generated varnames

src/plugins/e-acsl/TODO

src/plugins/e-acsl/configure.ac

src/plugins/e-acsl/env.ml

src/plugins/e-acsl/env.mli

...ins/e-acsl/tests/e-acsl-runtime/oracle/arith.1.res.oracle

...ugins/e-acsl/tests/e-acsl-runtime/oracle/arith.res.oracle

...ins/e-acsl/tests/e-acsl-runtime/oracle/array.1.res.oracle

...lugins/e-acsl/tests/e-acsl-runtime/oracle/at.1.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/at.res.oracle

...gins/e-acsl/tests/e-acsl-runtime/oracle/cast.1.res.oracle

...-acsl/tests/e-acsl-runtime/oracle/comparison.1.res.oracle

...ests/e-acsl-runtime/oracle/function_contract.1.res.oracle

.../tests/e-acsl-runtime/oracle/function_contract.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_arith.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_arith2.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_array2.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_at.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_at2.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_cast2.c

...gins/e-acsl/tests/e-acsl-runtime/oracle/gen_comparison2.c