Since long, the compiled code of stored routines has been printed in the trace file
when starting mysqld with the "--debug" flag. (At creation time only, and only in
debug builds of course.) This has been helpful when debugging stored procedure
execution, but it's a bit awkward to use. Also, the printing of some of the
instructions is a bit terse, in particular for sp_instr_stmt where only the command
code was printed.

This improves the printout of several of the instructions, and adds the debugging-
only commands "show procedure code <name>" and "show function code <name>".
(In non-debug builds they are not available.)