Add some xfailed estr tests.

Author: graydon

src/test/run-pass/estr-internal.rs

@@ -0,0 +1,9 @@
+// xfail-test
+fn main() {
+    let x : str/5 = "hello"/5;
+    let y : str/5 = "there"/_;
+    let mut z = "thing"/_;
+    z = x;
+    assert z[1] == 'h' as u8;
+    assert z[4] == 'g' as u8;
+}

src/test/run-pass/estr-shared.rs

@@ -0,0 +1,4 @@
+// xfail-test
+fn main() {
+    let x : str/@ = "hello"/@;
+}

src/test/run-pass/estr-slice.rs

@@ -0,0 +1,8 @@
+// xfail-test
+fn main() {
+    let x : str/& = "hello";
+    let mut y = "there";
+    y = x;
+    assert y[1] == 'h' as u8;
+    assert y[4] == 'e' as u8;
+}

src/test/run-pass/estr-uniq.rs

@@ -0,0 +1,4 @@
+// xfail-test
+fn main() {
+    let x : str/~ = "hello"/~;
+}