install-spotify: use master as repo on master branch
Remove the safe_run usage

Since the error trap provides more useful feedback info than safe_run
the latter is not needed, and actually makes the error messages less
informative.
Simplify usage() function
Make functions more visible.

Use the 'function' syntactic sugar and double spaces a la python
to markup functions. Single blank lines are used to delimit sections
within functions, so double newlines between them does make sense.
err_trap: refer to tracker URL
Don't hardcode issue tracker url
Clean up MAKE_TARBALL definitions
Remove RPM_NAME symbolic constant

It's not likely to change, and not likely to work if changed.
Make all variables local