Add <yconst> to the list of ignored wrapper elements

The <yconst> element started to appear in the XML after comment
processing started to be implemented in ycpc.
Don't call deep_copy for strings, terms and paths

Fixes #29.
Use ruby equivalent for Ops.equal and non_equal.

It works same, so it just makes code more beatiful.
Merge pull request #31 from yast/ops_equal2

Use ruby equivalent for Ops.equal and non_equal.
Merge branch 'less-deep-copy'
Merge branch 'master' into comments

Conflicts:
	lib/y2r/parser.rb