Returns the set of extensions known to indicate an executable file type on systems which require that (currently mswindows).

Checks the specified file to see if it is executable or if by appending one of the +executableExtensions it can be made executable. The return value is the actual executable path or nil if the file cannot be executed.

Returns the launch path for a tool given the name of a tool.
Locates the tool by looking in the standard directories and, if not found there, looking in the PATH set in the environment.
On ms-windows, this also tries appending common executable path extensions to the tool name in order to find it.
Returns the path found, or nil if the tool could not be located.