Forbid '=' as a cmp_ok operator

[dolmen]

Using '=' as an operator is always a user mistake, as he probably wants '==' instead.
This mistake is currently not visible if $got is an lvalue.

Here is an example where Test::More should die in first test:

use Test::More tests => 1;
my @arr;
cmp_ok(scalar @arr, '=', 3);
cmp_ok(scalar @arr, '==', 0);

[dolmen]

All other assignment operators should be forbiden too: += .= x= ^= |= ||= &&= ...

[schwern]

I concur. Assignment operators don't make much sense.

I don't know how far to take this. '=' vs '==' is an obvious trap. The rest not so much. I'd prefer a blacklist over a whitelist, as that allows people to get creative with comparison ops we haven't thought of (or get added like smartmatch).

[wolfsage]

#278

[schwern]

Merged into the master branch, thanks!