Added default impls for container methods

[sfackler]

A couple of implementations of Container::is_empty weren't exactly
self.len() == 0 so I left them alone (e.g. Treemap).

[sfackler]

Looks like a trie test fails. I'm looking into it.

[thestinger]

It's possible that there are still default method bugs blocking this.

[sfackler]

Looks like there are still some bugs:

rust: task failed at 'assertion failed: `(left == right) && (right == left)` (left: `1`, right: `0`)', /Users/sfackler/Documents/no_scan/code/rust/src/libstd/trie.rs:456
rust: task failed at 'explicit failure', /Users/sfackler/Documents/no_scan/code/rust/src/libstd/task/mod.rs:747
rust: task failed at 'assertion failed: `(left == right) && (right == left)` (left: `Some(4302215072)`, right: `Some(2)`)', /Users/sfackler/Documents/no_scan/code/rust/src/libstd/trie.rs:529
test str::tests::test_trim_left_chars ... ok

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x000000000000000a
[Switching to process 32918 thread 0x20b]
0x00000001001fe714 in trie..TrieNode$LT$uint$GT$::_a48e69e59d886de1::glue_drop_39521 ()
(gdb)

@msullivan mentioned that he's making a new snapshot for the default method fixes, so maybe that'll help?

[sfackler]

It seems to be working fine after a rebase. I may have not had @msullivan's fix last time.

[bluss]

If it depends on sully's fix, then you may have to wait after a snapshot?

[huonw]

(There's a snapshot with those fixes in the queue: #8050)

[sfackler]

It seems to be working fine on the current snapshot after rebasing.