Make PYENV_DEBUG imply -v for `pyenv install` (#2347)

Trace logs without `-v` are usually useless due to missing the build part.
So this leaves one less thing for users to worry about
when submitting error reports.

Mentioning `-v` in the issue template should stay for some time
since users report on old versions, too.

plugins/python-build/bin/pyenv-install

@@ -73,6 +73,8 @@ unset VERBOSE
 unset HAS_PATCH
 unset DEBUG
 
+[ -n "$PYENV_DEBUG" ] && VERBOSE="-v"
+
 parse_options "$@"
 for option in "${OPTIONS[@]}"; do
   case "$option" in