home-environment: use nix-env from PATH

It is safest to use the system install of Nix since that will be
compatible with the running nix-daemon and/or databases.

Also add a printout of the used Nix version in the activation script
when running in verbose mode.

Fixes #218.

modules/lib-bash/activation-init.sh

@@ -1,3 +1,5 @@
+#!/usr/bin/env bash
+
 function setupVars() {
     local profilesPath="/nix/var/nix/profiles/per-user/$USER"
     local gcPath="/nix/var/nix/gcroots/per-user/$USER"
@@ -46,6 +48,11 @@ else
     export DRY_RUN_CMD=""
 fi
 
+if [[ -v VERBOSE ]]; then
+    echo -n "Using Nix version: "
+    nix-env --version
+fi
+
 $VERBOSE_ECHO "Activation variables:"
 if [[ -v oldGenNum ]] ; then
     $VERBOSE_ECHO "  oldGenNum=$oldGenNum"