Add support for shell files without .sh suffix

[Anachron]

The shell-language plugin only works on files with the .sh suffix by default. At least on Linux a file doesn't need this suffix in order to be a valid shell file.

What I rather suggest is allowing to check the first line to be either !/bin/sh or !/usr/bin/env sh (or bash).

[rxi]

Note the change in this commit depends on functionality from the master/unreleased-1.08 version of lite