Throw error if unquoted attribute value is made up of more than one node

Resolves https://github.com/tildeio/htmlbars/issues/182.

The deleted lines in `token-handlers.js` were redundant and were mostly removed just to clean it up a bit.  But line 89 in particular needed to go because otherwise we wouldn't be able to get the line number with something like `class={{foo}}bar` (by the time we get to adding `bar` we'd no longer be on an attribute with a mustache from which to get the line number). 
That causes a failed test on cases like <img foo={{bar}} name="Bob"> .  In general the tokenizer does do that, but I think (still getting familiarized with the program flow) mustaches don't get passed to it, so in this case we need to do it there.  The failed test is actually `Components` in `parser-test.js`, which tests a complicated set-up.  I'll add a simple case like this to `html-compiler-test.js`, so that if the problem comes up in the future it'll point right at the problem, and amend the commit with it.