TILES-571 – Please make the significance of underscore (_) in tiles definition filename more obvious
SPR-11491 – Doc: Tiles 3 and underscores in definition names

<quote> 
… it looks like there is an issue with PostfixedApplicationResource.
 
This issue comes from SpringWildcardServletTilesApplicationContext#getResources(String) -> URLApplicationResource(String, URL) constructor -> super PostfixedApplicationResource(String localePath) constructor. When there is an
underscore, the string after the last underscore is identified as the locale. But clearly it's not a locale and one should be able to load /WEB-INF/base_tiles.xml.
</quote>

Along with improving the documentation the following code changes have been made
• if the resource name contains "_" and after it there is no supported locale language code then the whole resource name is treated as a non-localized path.
        This situation prints a warning like 
      		> No supported matching language for locale "zz". Using /my/path_zz.html as a non-localized resource path.
• if the resource name contains "_" and after it there is a supported locale language code but the locale constructed isn't valid/supported then the closest supported locale is used. This situation prints a warning like         > 
For resource /my/path_en_ZZ.html the closest supported matching locale to "en_ZZ" is "en". Using /my/path.html as resource path. 


git-svn-id: https://svn.apache.org/repos/asf/tiles/request/branches/TREQ_1_0_X@1583141 13f79535-47bb-0310-9956-ffa450edef68