Cleanup: Spelling Mistakes

This patch fixes many minor spelling mistakes, all in comments or
console output. Mostly contractions like can't, won't, don't, its/it's,
etc.

Differential Revision: https://developer.blender.org/D11663

Reviewed by Harley Acheson

source/blender/editors/mesh/editmesh_loopcut.c

@@ -223,7 +223,7 @@ static void ringsel_finish(bContext *C, wmOperator *op)
 
         EDBM_selectmode_flush_ex(lcd->em, SCE_SELECT_VERTEX);
       }
-      /* we cant slide multiple edges in vertex select mode */
+      /* we can't slide multiple edges in vertex select mode */
       else if (is_macro && (cuts > 1) && (em->selectmode & SCE_SELECT_VERTEX)) {
         EDBM_selectmode_disable(lcd->vc.scene, em, SCE_SELECT_VERTEX, SCE_SELECT_EDGE);
       }