bin/mdw-build: Discard `tar' errors when searching for `.../RELEASE'.
GNU `tar' reports a vague `write error' as a result of the broken pipe
caused by the following `grep' finding a successful match. This isn't
useful. In our case, we don't care about this, since either we've found
the file anyway (so we're happy) or we didn't (in which case we'll fail
anyway).
The report, which makes its way to stderr even in quiet mode, is
worrying until you learn to ignore it, at which point it may hide a more
serious problem.
~mdw / profile / commit