Is how've a word?

Every spell check / auto fill I come across does not recognize this word. However, in speech I find it used quite often as in

How've you been? (How have you been?)

So is this an accepted contraction or not?

What about these:

Where've (you been?) What've (you been up to?) Who've (you been talking to?)

MS Word 2010 seems to recognize "How've" as in "How've you been?" while Firefox tries to correct it to "Who've."

Google ngram viewer shows these in reasonably common usage, especially in more recent decades, but not nearly as often as their uncontracted counterparts (which makes sense for books).

These seem to be in line with "would've," an explicit example in the Chicago Manual of Style (as a word).

Finally, remember the most important consideration is whether or not the intended meaning behind your communication will be clear in the context you're communicating. In most cases, the intended meaning of these contractions will be clear.