Add documentation to stripping of tar path (alexcrichton#220)

tar-rs will strip any current directory out of the paths users are
passing into the API. This documents that behavior and adds a test
to ensure the documented behavior.

src/header.rs

@@ -362,7 +362,8 @@ impl Header {
     ///
     /// This function will set the pathname listed in this header, encoding it
     /// in the appropriate format. May fail if the path is too long or if the
-    /// path specified is not Unicode and this is a Windows platform.
+    /// path specified is not Unicode and this is a Windows platform. Will
+    /// strip out any "." path component, which signifies the current directory.
     pub fn set_path<P: AsRef<Path>>(&mut self, p: P) -> io::Result<()> {
         self._set_path(p.as_ref())
     }
@@ -414,7 +415,8 @@ impl Header {
     ///
     /// This function will set the linkname listed in this header, encoding it
     /// in the appropriate format. May fail if the link name is too long or if
-    /// the path specified is not Unicode and this is a Windows platform.
+    /// the path specified is not Unicode and this is a Windows platform. Will
+    /// strip out any "." path component, which signifies the current directory.
     pub fn set_link_name<P: AsRef<Path>>(&mut self, p: P) -> io::Result<()> {
         self._set_link_name(p.as_ref())
     }

tests/header/mod.rs

@@ -139,6 +139,12 @@ fn set_path() {
         assert_eq!(t!(h.path()).to_str(), Some("foo\\bar"));
     }
 
+    // set_path documentation explictly states it removes any ".", signfying the
+    // current directory, from the path. This test ensures that documented
+    // beavhior occurs
+    t!(h.set_path("./control"));
+    assert_eq!(t!(h.path()).to_str(), Some("control"));
+
     let long_name = iter::repeat("foo").take(100).collect::<String>();
     let medium1 = iter::repeat("foo").take(52).collect::<String>();
     let medium2 = iter::repeat("fo/").take(52).collect::<String>();