setup_cabal.sh - correct usage of $APT_GET in install_package

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
git-grep-filter - chain `grep -v` to `git grep`

Previously, we would do:

    git grep -n 'org_pattern' > tmpfileOne
    cat tmpfileOne | grep -v 'exclude1' | grep -v 'exclude2' > tmpfileTwo
    grep --color=always 'org_pattern' tmpfileTwo | less -R

Now this becomes:

    git grep -n 'org_pattern' | grep -v 'exclude1' | grep -v 'exclude2' > tmpfileOne
    grep --color=always 'org_pattern' [ran through a truncate line filter]
    cat tmpfileTwo | less -R

which avoids the need to send the output of `git grep` to a file, then `cat`
that file and pass it through the `grep -v` filters. This should be slightly
faster.

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>