add Regexp type as a possible array element in the function "member"

This commit adds Regexp type as a possible array element in the function "member".
Unfortunately, regexp cannot be passed to functions in puppet, so you will get syntax error if you try to use it this way:
``` puppet
member(['foo',/bar/],'buzz')
```
However, it will work if used together with hiera or loadyaml:
``` puppet
# example.yaml
#
# array:
#  - a
#  - !ruby/regexp '/^foo$/'

$myhash = loadyaml('example.yaml')
member(['a','b',$myhash['array']], 'foo')