Crowd permits adding user attributes that are not valid LDAP attribute names

Steps to reproduce:

1. Log into crowd;
2. Select 'Users' --> Click on username --> select 'Attributes' tab
3. Enter an invalid LDAP attribute name, such as '_invalid'
4. Click 'Add >>" button

The same issue exists in the REST API.

The rules for well-formed LDAP attribute names are described by the 'keystring' production of the grammar, see http://tools.ietf.org/html/rfc4512#section-1.4