Apply spelling corrections following Even's parallel commit c95c7735.
The patch couldn't be cherry-picked because of his changes to tools/unsupported/CMakeLists.txt which doesn't exist in this repo.  There are a few places where I think a spelling fix was done incorrectly or where something appears to have been missed.  I'm not sure why in some cases British spelling is changed to American spelling, but I'm following them.  As for changing the spelling in ChangeLog it causes the ChangeLog to diverge from the commit log messages, and that's fine, but could lead to difficulty later in comparing ChangeLog to commit log messages.