clean up pyenv plugin

This commit cleans up the pyenv plugin to follow the newer conventions of the
other *env plugins, as well as addresses the changes made to pyenv for PATH
munging.

plugins/available/pyenv.plugin.bash

@@ -2,14 +2,33 @@
 cite about-plugin
 about-plugin 'load pyenv, if you are using it'
 
-export PYENV_ROOT="$HOME/.pyenv"
-pathmunge "$PYENV_ROOT/bin"
+# https://github.com/pyenv/pyenv
 
-if _command_exists pyenv; then
-	eval "$(pyenv init - bash)"
+# Load after basher
+# BASH_IT_LOAD_PRIORITY: 260
+
+# Don't modify the environment if we can't find the tool:
+# - Check if in $PATH already
+# - Check if installed manually to $PYENV_ROOT
+# - Check if installed manually to $HOME
+_command_exists pyenv \
+	|| [[ -n "$PYENV_ROOT" && -x "$PYENV_ROOT/bin/pyenv" ]] \
+	|| [[ -x "$HOME/.pyenv/bin/pyenv" ]] \
+	|| return 0
+
+# Set PYENV_ROOT, if not already set
+export PYENV_ROOT="${PYENV_ROOT:-$HOME/.pyenv}"
+
+# Add PYENV_ROOT/bin to PATH, if that's where it's installed
+if ! _command_exists pyenv && [[ -x "$PYENV_ROOT/bin/pyenv" ]]; then
+	pathmunge "$PYENV_ROOT/bin"
 fi
 
-#Load pyenv virtualenv if the virtualenv plugin is installed.
+# Initialize pyenv
+pathmunge "$PYENV_ROOT/shims"
+eval "$(pyenv init - bash)"
+
+# Load pyenv virtualenv if the virtualenv plugin is installed.
 if pyenv virtualenv-init - &> /dev/null; then
 	eval "$(pyenv virtualenv-init - bash)"
 fi