core - issue in calculating hasEditPermission

Currently, the ORM translation of the SQL query that is made to the
database to check whether a user can edit a MD or not (depending on
which group he belongs to) is the following:

"SELECT
  ...
FROM
  ...
WHERE
  user is EDITOR
AND
  userID = id
AND
  groupID = x AND groupID = y AND groupID = z ..."

The correct request that has to be made should end up with
"[...]
AND
  groupID IN (x,y,z,...)"
instead.

The following patch implements this "IN / OR" logic.
Tested manually, but please review.
Test:
* login admin
* create group : G1, G2
* create MD1 editable by G1
* create user : U1
* U1 can edit MD1 : ok
* set MD1 editable by  G1 and G2
* U1 cant edit MD1 : failure

After applying your patch, on search when logged in I get that exception :
```
2014-07-25 18:40:11,553 DEBUG [org.hibernate.SQL] - select usergroup0_.groupId as groupId1_39_, usergroup0_.profile as profile2_39_, usergroup0_.userId as userId3_39_ from UserGroups usergroup0_ where usergroup0_.profile=? and usergroup0_.userId=5069 and (usergroup0_.groupId in (5068 , 5067))
2014-07-25 18:40:11,555 ERROR [jeeves.service] - Exception when executing service
2014-07-25 18:40:11,555 ERROR [jeeves.service] -  (C) Exc : org.springframework.dao.IncorrectResultSizeDataAccessException: result returns more than one elements; nested exception is javax.persistence.NonUniqueResultException: result returns more than one elements
2014-07-25 18:40:11,588 DEBUG [jeeves.service] - Raised exception while executing service
<error id="error">
  <message>result returns more than one elements; nested exception is javax.persistence.NonUniqueResultException: result returns more than one elements</message>
  <class>IncorrectResultSizeDataAccessException</class>
  <stack>
    <at class="org.springframework.orm.jpa.EntityManagerFactoryUtils" file="EntityManagerFactoryUtils.java" line="307" method="convertJpaAccessExceptionIfPossible" />
    <at class="org.springframework.orm.jpa.vendor.HibernateJpaDialect" file="HibernateJpaDialect.java" line="108" method="translateExceptionIfPossible" />
    <at class="org.springframework.orm.jpa.AbstractEntityManagerFactoryBean" file="AbstractEntityManagerFactoryBean.java" line="403" method="translateExceptionIfPossible" />
    <at class="org.springframework.dao.support.ChainedPersistenceExceptionTranslator" file="ChainedPersistenceExceptionTranslator.java" line="58" method="translateExceptionIfPossible" />
    <at class="org.springframework.dao.support.DataAccessUtils" file="DataAccessUtils.java" line="213" method="translateIfNecessary" />
    <at class="org.springframework.dao.support.PersistenceExceptionTranslationInterceptor" file="PersistenceExceptionTranslationInterceptor.java" line="163" method="invoke" />
    <at class="org.springframework.aop.framework.ReflectiveMethodInvocation" file="ReflectiveMethodInvocation.java" line="172" method="proceed" />
    <at class="org.springframework.data.jpa.repository.support.LockModeRepositoryPostProcessor$LockModePopulatingMethodIntercceptor" file="LockModeRepositoryPostProcessor.java" line="92" method="invoke" />
    <at class="org.springframework.aop.framework.ReflectiveMethodInvocation" file="ReflectiveMethodInvocation.java" line="172" method="proceed" />
    <at class="org.springframework.aop.interceptor.ExposeInvocationInterceptor" file="ExposeInvocationInterceptor.java" line="91" method="invoke" />
    <skip>...</skip>
    <at class="org.fao.geonet.kernel.AccessManager" file="AccessManager.java" line="443" method="hasEditPermission" />
```

So I would suggest 
```
        return _userGroupRepository.findAll(spec) != null;
``` 

here ?