Deal with Bash `unset`'s `-v` and `-f` flag.

[JoaoCostaIFG]

Unset in bash is able to alternate between unsetting functions and variables, using the -f and -v flags, respectively.

This fixes a problem where babelfish would translate unset -f foo to set -e -f; set -e foo. The correct translation would be functions -e foo.

[joaolucasmartins]

I also need this fix, merge plz