GEOS-5844 fix nulls in SecureCatalog.list

a catalog filter can potentially result in nulls being in the
returned iterator. an example is a LocalWorkspaceCatalogFilter
when a WMS virtual service getcaps request occurs.

forward port from 5edc2cc67de9aa922c798c1e8049939178a9d529

had to add means to override check on GeoServerSecurityManager
so test cases would not depend on full spring context
GEOS-5849 added localized rule labels support to GetLegendGraphic output
GEOS-5847 fixed issue with nested layergroups
Ensure network links are always getting downloaded, without shrinking the bbox
Merge pull request #253 from mbarto/geos5849_internationalized_getlegendgraphic

GEOS-5849 added localized rule labels support to GetLegendGraphic output
Merge pull request #250 from ischneider/GEOS-5844

GEOS-5844 fix nulls in SecureCatalog.list
GEOS-5851 Make sure we don't synch up computing a non cacheable feature type each time we need a feature source
Fix build
GEOS-5852 default filter chain does not create HTTP session even with session creation enabled
Security documentation enhancments
Merge pull request #255 from mbarto/geos_5847_jde

GEOS-5847 fixed issue with nested layergroups
trying fixing the build after GEOS-5847 broke it
GEOS-5862 - GSUSER variable not available in REST requests
GEOS-5863 Add support for white space margin in graphic fills
Unit tests for DataSourceFactoryBean and support for JNDI lookup of DataSource
Logging, and making mockJDBCDriver Java 7 ready
Support multiple SortBy on JDBCCatalogFacade
Ignore testcase used for debugging but lacking asserts to get test coverage right.
Revised query for list with SortBy on JDBCCatalogFacade
Tidying some warnnings