Problem: When virtcol() gets a column that is not the first byte of a
multi-byte character the result is unpredictable. (Christian
Ludwig)
Solution: Correct the column to the first byte of a multi-byte character.
Change the utf-8 test to new style.
Problem: Using the system default encoding makes tests unpredictable.
Solution: Always use utf-8 or latin1 in the new style tests. Remove setting
encoding and scriptencoding where it is not needed.
Problem: syn-cchar defined with matchadd() does not appear if there are no
other syntax definitions which matches buffer text.
Solution: Check for startcol. (Ozaki Kiichi, haya14busa, closes#757)
