Add check that specified GitBash path points to bash, not for any other .exe

[introfog]

Right now, you can specify path to any .exe instead of path to GitBash. In that case when you will run command, console window will be opened for one moment (because an error occurred during running).

In the scope of the issue, add an internal check that path is points to GitBash, it can be done by calling PATH_TO_GIT_BASH --version and checking that output contains for instance word bash or smth like that.