Reviewed by Xan Lopez and Gustavo Noronha.

        Set user-agent from application
        https://bugs.webkit.org/show_bug.cgi?id=17375

        Add 'user-agent' setter/getter API to WebSettings.

        * WebCoreSupport/FrameLoaderClientGtk.cpp:
        (WebKit::FrameLoaderClient::FrameLoaderClient):
        (WebKit::FrameLoaderClient::userAgent):
        * WebCoreSupport/FrameLoaderClientGtk.h:
        * webkit/webkitprivate.h:
        * webkit/webkitversion.h.in:
        * webkit/webkitwebsettings.cpp:
        (webkit_get_user_agent):
        (webkit_web_settings_class_init):
        (webkit_web_settings_finalize):
        (webkit_web_settings_set_property):
        (webkit_web_settings_get_property):
        (webkit_web_settings_copy):
        (webkit_web_settings_get_user_agent):
        * webkit/webkitwebsettings.h:
        * webkit/webkitwebview.cpp:
        (webkit_web_view_dispose):

        Define UA version macros to be used by the UA string.
        Add new WebSettings unit test for the User-Agent string API.

        * GNUmakefile.am:
        * configure.ac:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@45531 268f45cc-cd09-0410-ab3c-d52691b4dbfc