An exclude filter is basically a 'wildcard but foo', so even if a
childMayMatch, other children of a dir may not, therefore childMayMatch
does not matter, but we should not go down unless the dir is selected
for restore.
This improves restore performance by several orders of magniture by not
going through the whole tree recursively when we can anticipate that no
match will ever occur.
Internally rename restorer.Filter -> restorer.SelectForRestore to make
semantic clear.
In addition, swap parameters to filepath.Match() so that the pattern can
really be matched.
Limitation: The filter only works on the filename, not on any path
component, e.g. '*.go' selects all go files, 'subdir/foo*' doesn't
select anything.
Fixes#202.
This just matches the passed pattern against the full source path with
filepath.Match which, in contrast go filepath.Glob, doesn't match the
directory separator with '*' and is not terribly useful that way.
Someone should replace that by a more sophisticated matcher.
