Do not abuse argv[0] to supply roles and IDs to SMP kids (#176)

Do not abuse argv[0] to supply roles and IDs to SMP kids (#176)

Use a newly added "--kid role-ID" command line option instead. Just like
argv[0], the new option is not meant for direct/human use.

This change allows exec(3)-wrapping tools like Valgrind to work with SMP
Squid: When launching kid processes, Valgrind does not pass Squid-formed
argv[0] to kid processes, breaking old kid role and ID detection code.

This change does not alter argv[0] of Squid processes. There is nothing
wrong with Squid-formed argv[0] values for Squid kids.

Also added a CommandLine class to support command line parsing without
code duplication. Squid needs to handle the new --kid option way before
the old mainParseOptions() handles the other options. The new class also
encapsulates argv manipulations, reducing main.cc pollution.