Better shebang portability

Use env(1) to locate shell binary (see http://en.wikipedia.org/wiki/Shebang_%28Unix%29#Portability) - so it would work fine in FreeBSD and other systems with bash(1) binary placed not at /bin/bash, but at /usr/bin/bash, /usr/local/bin/bash or somewhere other.
Merge pull request #54 from rc5hack/patch-1

Better shebang portability