word choice - "His head" or "their head"?

I was disappointed to see a favorite storybook from my childhood has been edited. (Harry, the Dirty Dog; ISBN-13: 978-0064430098) I distinctly remember the text written as follows:

...but everyone shook his head and said, "Oh, no, it couldn't be Harry."

I was taught that the male gender form takes precedence, when speaking several individuals of each gender. However, the book was edited to read,

...but everyone shook his head their head and said, "Oh, no, it couldn't be Harry."

ARGH! Please assure me that the original version and I are correct! There are some other minor edits that have simply ruined the book for me. (My linguistic snobbery helped, too.)

Answer

I believe the edited version is incorrect.
It should be "but everyone shook their head" (singular head, for each individual. Unless you're dealing with a hydra :P)

The male dominance in pluralisation that you mentioned is still correct, but is avoided to not offend feminists, and will likely be phased out for the same reason.