Included targets in cabal's bash-completion.

When commpleting for cabal build/repl/test/bench, this completes the possible
targets depending on their types.  This is a temporary workaround, the
definitive solution would be to include those targets in cabal itself, via
``--list-options''.

In other words, when typing "cabal repl [tab]", only option arguments (starting with --) are offered for completion.  This commit solves that by adding possible targets to the list.

As mentioned before, this is a temporary workaround, code searches in current directory for a ".cabal" file and "parses" it to know which targets to complete.

This partially solves issue #1382