Small code improvements for readability, code size, and/or speed.

Small code improvements for readability, code size, and/or speed.

BINARY_SUBSCR:
    * invert test for normal case fall through
    * eliminate err handling code by jumping to slow_case

LOAD_LOCALS:
    * invert test for normal case fall through
    * continue instead of break for the non-error case

STORE_NAME and DELETE_NAME:
    * invert test for normal case fall through

LOAD_NAME:
    * continue instead of break for the non-error case

DELETE_FAST:
    * invert test for normal case fall through

LOAD_DEREF:
    * invert test for normal case fall through
    * continue instead of break for the non-error case