Fix typo in rmbranch alias.
Better copy/paste interop for tmux 1.8 and OS X

<prefix> Ctrl-c : copy into system clipboard
<prefix> Ctrl-v : tmux paste from system clipboard

In tmux copy-mode:

v : begin selection (same as "space")
y : yank into both tmux buffer and system clipboard
Merge pull request #14 from rondale-sc/master

Fix typo in rmbranch git alias.