Prevent false positives

[nferraz]

This pull request will prevent false positives in contexts that cannot generate SQL injections, for instance:

die     "Select returned: $error";
warn    "Update returned: $error";
croak   "Insert returned: $error";
carp    "Delete returned: $error";
confess "Select returned: $error";

It will always look at the previous significant sibling, so it will also prevent false positives like:

do_something() or die     "Select returned: $error";
do_something() or warn    "Update returned: $error";
do_something() or croak   "Insert returned: $error";
do_something() or carp    "Delete returned: $error";
do_something() or confess "Select returned: $error";

[coveralls]

Coverage decreased (-0.4%) to 96.622% when pulling 7d6b813 on nferraz:nferraz/prevent-false-positives into 13fa7f0 on guillaumeaubert:master.

[xsawyerx]

The travis-ci tests are failing for unrelated reasons:

$ perlbrew use 5.16

ERROR: The installation "5.16" is unknown.

and:

$ perlbrew use 5.10

ERROR: The installation "5.10" is unknown.