Add SafeUri type, similar to SafeHtml but for values in a URL attribute context.

Support SafeUri-typed arguments in SafeHtmlTemplates.

Also added a few overloads in c.g.g.user.client.

Note that this is a breaking change in the sense that DataResource and
ImageResource have a new getSafeUri method, as well as overloaded constructors
taking URIs in the form of SafeUri.

Patch by: tbroyer
Review by: xtof
Fixes issues: 6145

Review at http://gwt-code-reviews.appspot.com/1447812


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10282 8db76d5a-ed1c-0410-87a9-c151d255dfc7
33 files changed