Single click buffer opening support

[honsiorovskyi]

Hello again! Here I have written a small patch to implement an opportunity to use a single click instead of a double click when opening a buffer.

This patch adds a global variable g:Buffetsingleclickloading. When it's empty the default behaviour (double click) is used, else a single click will take place.

The patch: https://gist.github.com/gonsiorovsky/6000233.

Regards,
Denis.