Fix multiple issues in Makefile

$RCZWC was never filled properly for the following reasons:

* echo generated one line also containing .zwc files and grep filtered
  that line: always empty.
* $ in sed wasn't working because of being in a Makefile and hence
  needs to be escaped as $$.
* | needs to be escaped in sed regexp.
* grep treats "." as special character, hence use fgrep.
Load zargs by default