Minor lint fixes

[SafariMonkey]

Fixes some Rust warnings:

• panic!(format!(...)) is redundant, as panic! supports formatting
• mem::replace expects its return value to be used, but it's dropped - I changed this to an assignment, but I'm not 100% sure if this is equivalent

Also fixes some "issues" in the Bash scripts, mostly reported by ShellCheck:

• it's good practice to quote variables, so I quoted the ones ShellCheck complained about
• there are some places where it complained about the exit code being suppressed, so I propagated it
  • it's not clear to me whether this is at all useful to you, as set -e and such isn't being used

[cantino]

Thanks @SafariMonkey!