Unused variables/variable typo's cleanup

[DD32]

Patch removed variables which are not used by any function, and corrects a number of typo's

There is also an undefined variable which i have not touched:
register_taxonomy() refers to an undefined variable $term; It looks like it should be the slug to me, but i'm not entirely sure of it, So i've left it unchanged:
​http://trac.wordpress.org/browser/trunk/wp-includes/taxonomy.php#L185

[DD32]

Few more notes:

• wp-includes/pluggable.php: get_avatar(); $defaults[$avatar_default][1] doesnt exist, As far as i could tell, 'custom' shouldnt be passed to that function, instead, a URL should be, So i've assumed that branch was supposed to add the size arg to the url..
• Most of those changes are untested, In the sense that the script I refer to for checking didnt come up with any other uses of the variables, And i couldnt locate anything which was refering to them.

[ryan]

(In [9716]) Unused var fixes. Props DD32. see #8220