Move glob implementation to new crate.

It is isolated and complex enough that it deserves attention all on its
own. It's also eminently reusable.

globset/src/pathutil.rs

@@ -0,0 +1,38 @@
+use std::ffi::OsStr;
+use std::path::Path;
+
+/// The final component of the path, if it is a normal file.
+///
+/// If the path terminates in ., .., or consists solely of a root of prefix,
+/// file_name will return None.
+#[cfg(unix)]
+pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
+    path: &'a P,
+) -> Option<&'a OsStr> {
+    use std::os::unix::ffi::OsStrExt;
+    use memchr::memrchr;
+
+    let path = path.as_ref().as_os_str().as_bytes();
+    if path.is_empty() {
+        return None;
+    } else if path.len() == 1 && path[0] == b'.' {
+        return None;
+    } else if path.last() == Some(&b'.') {
+        return None;
+    } else if path.len() >= 2 && &path[path.len() - 2..] == &b".."[..] {
+        return None;
+    }
+    let last_slash = memrchr(b'/', path).map(|i| i + 1).unwrap_or(0);
+    Some(OsStr::from_bytes(&path[last_slash..]))
+}
+
+/// The final component of the path, if it is a normal file.
+///
+/// If the path terminates in ., .., or consists solely of a root of prefix,
+/// file_name will return None.
+#[cfg(not(unix))]
+pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
+    path: &'a P,
+) -> Option<&'a OsStr> {
+    path.as_ref().file_name()
+}