Clarify that a PHUITagView API argument is boolean, not a value in "millimeters"

Summary:
See PHI454. Ref T13102. This parameter is not named as clearly as it could be.

This is a buff to API humor.

See also <https://secure.phabricator.com/differential/diff/46024/>.

Test Plan: Read API method, laughed aloud ("LAL") much harder because the humor was now less subtle. Subtle humor is unsuitable for this project.

Maniphest Tasks: T13102

Differential Revision: https://secure.phabricator.com/D19231

src/view/phui/PHUITagView.php

···
     return $this;
   }
 
-  public function setSlimShady($mm) {
-    $this->slimShady = $mm;
+  public function setSlimShady($is_eminem) {
+    $this->slimShady = $is_eminem;
     return $this;
   }