Update plenv.sh
Merge pull request #1 from rkleemann/patch-1

Update plenv.sh
Make setup more resilient

Handle case where PLENV_ROOT is already set to something else, and call full path to plenv executable.
Merge pull request #2 from rkleemann/patch-2

Make setup more resilient
Merge branch 'master' into debian-package

Conflicts:
	Makefile
Merge remote-tracking branch 'gdey/debian-package' into debian-package

Conflicts:
	Makefile