When searching directories recursively, it's still
desirable to filter the contents by the file pattern,
so that 'g foo /sys/src' doesn't end up searching for
foo within .$O files.
Files passed explicitly are still searched, so for the
old behavior, just use walk:
g foo `{walk -f $dir}
This allows us to 'g' the files
within a directory, as in:
g _MAX /sys/include/ape
Before this change, we'd attempt to
grep the directory structure, which
is not ideal. After, we grep the
files within the directory.
