Make xolox#easytags#filetypes#add_group() easier to understand
Bug fix for xolox#easytags#define_tagkind() invocations

It should be given a canonical file type and since I just changed the
canonical file type for C to be C++ the invocations should be updated
as well. This should really have been part of the change set with id
9b6e7d125c660f31091f59b52de9b1e425cbcb64. That's what I get for not
testing properly...

See also issue #91 on GitHub:
  https://github.com/xolox/vim-easytags/issues/91
Bug fix for xolox#easytags#filetypes#find_ctags_aliases()

When a canonical Vim file type mapped to a group of file types,
the group was returned without the canonical file type :-s

See also issue #91 on GitHub:
  https://github.com/xolox/vim-easytags/issues/91