move_word is inconsistent on last letter of a word

[sgrj]

This affects the master version, and manifests in different ways.

1. Pressing alt-d on the last letter of a word deletes the last letter and the trailing whitespace, whereas alt-d on any other letter only deletes until the end of the word. E.g., given

abc def

when the cursor is on c, then alt-d results in

abdef

while when the cursor is on b, then alt-d results in

a def

2. Using the w motion in vi mode on the last letter of a word moves the cursor to the second letter of the next word, whereas w on any other letter moves to the first letter of the next word. E.g., given

abc def

when the cursor is on c, then w moves the cursor to e, while when the cursor is on a or b, then w moves the cursor to d.

3. This is also the root cause for vi binding 'e' has wrong behaviour on second-to-last char #4025 (the description there is outdated: after ce65709, when the cursor is on 1 in 12 345, the cursor moves to the space, but it should move to the 2)