* contrib/compare_tests: Eliminate Shellcheck warnings.

	* contrib/compare_tests: Eliminate Shellcheck warnings.
	* contrib/mysql/sum2xml.sh: Likewise.

Warnings fixed:
	Use single quotes, otherwise this expands now rather than when signalled. [SC2064]
	Trapping signals by number is not well defined. Prefer signal names. [SC2172]
	SIGKILL/SIGSTOP can not be trapped. [SC2173]
	Trapping signals by number is not well defined. Prefer signal names. [SC2172]
	Check exit code directly with e.g. 'if mycmd;', not indirectly with $?. [SC2181]
	read without -r will mangle backslashes. [SC2162]
	egrep is non-standard and deprecated. Use grep -E instead. [SC2196]