[vim] Fix error when dd the only line.

When the buffer has only one line, pressing 'dd' causes
CodeMirror to throw an error "There is no line -1".
Properly take gutter borders and margins into account when sizing gutter markers

Issue #2836
SQL hint support for backticks for column/table names

Signed-off-by: Nisarg Jhaveri <nisarg.jhaveri@research.iiit.ac.in>
[sql mode] Tokenize unclosed backtick-escapes more intelligently
Merge branch 'master' of https://github.com/codemirror/CodeMirror into sql_hint