Fix which command on ubuntu

[fbernier]

Hi, the 'which' command has no option '-s' on my system (ubuntu 12.10). which makes the command fail and return a bad exit status. I figured just redirecting the output to /dev/null would fix this issue for me while remaining compatible with OSX.

[toy]

Hi François,
This will not work as > will be escaped, try system(*%W[which man > /dev/null]).
Also I think it is better to extract this system call to private method like bin_accessible?(bin).

[fbernier]

Indeed I did this way too quickly. I'll come up with something later.