Add virtcol parameter for col_current segment

The virtual column number is also default. I doubt anybody here ever
wanted to see byte offset. When it comes to a questions like alignment,
forced text width and so on only virtual columns matter. It would be
good to optionally take concealed characters into account, but vim does
not provide a way to do so (well, except recent screencol() added solely
for testing which would be hard, but not impossible, to adapt to such
needs).

Closes #25.

powerline/ext/vim/segments/core.py

@@ -8,6 +8,7 @@ from powerline.lib.memoize import memoize
 
 vim_funcs = {
 	'col': vim_get_func('col', rettype=int),
+	'virtcol': vim_get_func('virtcol', rettype=int),
 	'expand': vim_get_func('expand'),
 	'line': vim_get_func('line', rettype=int),
 	'mode': vim_get_func('mode'),
@@ -163,7 +164,10 @@ def line_current():
 	return vim_funcs['line']('.')
 
 
-def col_current():
+def col_current(virtcol=True):
 	'''Return the current cursor column.
+
+	If the optional argument is True then returns visual column with concealed
+	characters ignored (default), else returns byte offset.
 	'''
-	return vim_funcs['col']('.')
+	return vim_funcs['virtcol' if virtcol else 'col']('.')