Uses shellescape for serializing options for `env`

Prevents environment variables containing quotes from breaking
commandlines when shelling out.
test for #229 also protect weird values
Merge pull request #231 from heroku/merge-229

Merge shellescaping fixes.
update changelog
bump to v104
update changelog
Revert "Uses shellescape for serializing options for `env`"

This reverts commit 911642f7c25c229bec8ff7f44876abd26bbee8be.

Conflicts:
	lib/language_pack/shell_helpers.rb
remove merge conflict
refactor env escaping

add unit tests
don't escape twice
don't shellescape shell variables
fix quotes
fix tests
Merge pull request #232 from heroku/schneems/fix-env-escape

refactor env escaping
bump to v107
use system env
do regex matching for shellescaping tests
Merge pull request #233 from heroku/env

use system env
proper formatting for pulling the patchlevel (adds the - before the p)
Merge pull request #230 from heroku/bundler_patchlevel

proper formatting for pulling the patchlevel (adds the - before the p)