PATCH: filtering the pastebuffer with an external program

[Adrian Pardini]

A while ago I hinted on geda-user that it'd be nice to have an action to filter the current selection / buffer with an external program (like ! in vim).

The following patches provide an initial implementation supporting only the pastebuffer. They add the actions

Filter(command)
! command

that run sh -c command , stdin is the contents of the pastebuffer. If the command returns 0 the pastebuffer is replaced with stdout, like "load layout data to paste-buffer" but without mode switch.