Make debugging dumps more consistent across Perl versions.

Makes them easier to compare.
Provide more diagnostic information for debugging this touchy test.
Skip tests about line numbers for computed defaults on earlier Perls.

5.10 and back probably set the line number after parsing a "line"
rather than per op code.  This might explain why Perl would often be
off by one in error reporting inside things like if statements.

The important thing is the body of the subroutine is correct, so I'm
skipping the tests for default line numbers on those Perls.  My yak
shears are dull.