Allow for cases where user might've aliased some programs

The $(type -p | head -1) construct expects to always get a path, so need to ignore such aliases with -P

Closes https://github.com/pyenv/pyenv/issues/1662

plugins/python-build/test/pyenv_ext.bats

@@ -89,7 +89,7 @@ install_tmp_fixture() {
 }
 
 resolve_link() {
-  $(type -p greadlink readlink | head -1) "$1"
+  $(type -P greadlink readlink | head -1) "$1"
 }
 
 run_inline_definition_with_name() {