Make to_str pure and fix const parameters for str-mutating functions

Two separate changes that got intertwined (sorry):

Make to_str pure. Closes #3691

In str, change functions like push_char to take an &mut str instead of
an &str. Closes #3710

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libcore/path.rs b/src/libcore/path.rs
index 6d023ed1bfb..e5d2397da0d 100644
--- a/src/libcore/path.rs
+++ b/src/libcore/path.rs
@@ -61,7 +61,7 @@ pub pure fn Path(s: &str) -> Path {
 }
 
 impl PosixPath : ToStr {
-    fn to_str() -> ~str {
+    pure fn to_str() -> ~str {
         let mut s = ~"";
         if self.is_absolute {
             s += "/";
@@ -236,7 +236,7 @@ impl PosixPath : GenericPath {
 
 
 impl WindowsPath : ToStr {
-    fn to_str() -> ~str {
+    pure fn to_str() -> ~str {
         let mut s = ~"";
         match self.host {
           Some(ref h) => { s += "\\\\"; s += *h; }