perl 1.0 patch 8: perl needed an eval operator and a symbolic debugger

perl 1.0 patch 8: perl needed an eval operator and a symbolic debugger

I didn't add an eval operator to the original perl because
I hadn't thought of any good uses for it.  Recently I thought
of some.  Along with creating the eval operator, this patch
introduces a symbolic debugger for perl scripts, which makes
use of eval to interpret some debugging commands.  Having eval
also lets me emulate awk's FOO=bar command line behavior with
a line such as the one a2p now inserts at the beginning of
translated scripts.