Use dir globbing to discover .clj files

[vemv]

orchard.namespace can iterate over potentially many, many files (200K+ for a specific user) to determine whether they're .clj files. That's slow enough to cause nrepl timeouts.

Using dir globbing would be faster https://stackoverflow.com/questions/9148528/how-do-i-use-directory-globbing-in-jdk7

See also https://docs.oracle.com/javase/8/docs/api/java/nio/file/FileSystem.html#getPathMatcher-java.lang.String-