gettext enhancements: Make it easier to use the right gettext

gettext enhancements: Make it easier to use the right gettext

This patch adds a check to insane to ensure that gettext exists in the
dependancy list when it is used in the configure.[ac|in]

Further we enhance the gettext class to enable easy addition of the required
gettext dependancies by inheriting the gettext class.

Signed-off-by: Joshua Lock <josh@linux.intel.com>