Improve fixture for "imports_on_separate_lines".

This should hove gone into 8fec4628174 already, but I missed adding.
Fix fix compound_statements: Remove trailing semicolon.

Up to this change a trailing semicolon created a superfluous newline,
while the semicolon should just have been removed. This is how it is
done now.
Minor cleanup: Change quotes and wrap lines to be more readable.
Cleanup: Evaluate often used stuff only once.