[MERGE] Add LRUCache.get()

[John Arbash Meinel]

I working on fixing up the pack => knit join code and wanted to use an
LRUCache for the parent texts. The Knit code expects to use
"texts.get(key, None)" so that it can fallback if it isn't present.
This implements similar behavior and adds a test for it.

John
=:->
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: text/x-patch
Size: 3759 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20071116/d00e2d05/attachment.bin