* Searching of first parental PSI elements before/after new line
correctly stops at the start/end of file. As result it's possible now
to surround element at the first/last line in the file.
Also corresponding traversal does not try to climb above PSI file.
* Even single character can be selected in first place.
* In languages that uses indentation to delimit blocks (like Python)
several consequent sibling statements can be surrounded even if the last
of them is at the end of its parent.
