Merge branch 'jc/local-extern-shell-rules'

Merge branch 'jc/local-extern-shell-rules'

Document and apply workaround for a buggy version of dash that
mishandles "local var=val" construct.

* jc/local-extern-shell-rules:
  t1016: local VAR="VAL" fix
  t0610: local VAR="VAL" fix
  t: teach lint that RHS of 'local VAR=VAL' needs to be quoted
  t: local VAR="VAL" (quote ${magic-reference})
  t: local VAR="VAL" (quote command substitution)
  t: local VAR="VAL" (quote positional parameters)
  CodingGuidelines: quote assigned value in 'local var=$val'
  CodingGuidelines: describe "export VAR=VAL" rule