Detect EOL visual block selections

[tommcdo]

When a visual block is created using $, it may result in a selection where the rightmost corners are not the rightmost edge of the visual block. Example:

hello
goodbye
hi

Since blocks are reproduced using '< and '>, the longer text in the middle lines may not be covered.

[tommcdo]

Using getregtype() seems to specify the maximum width of the visual block.