drop std:: qualifiers on more stl datatypes

We "using namespace std" anywhere we need a std::string or a std::vector.
make DiskInterfaceTest.StatBadPath quiet

Add a flag to temporarily suppress error output.

Fixes issue #281.
adjust the wording in "multiple rules generate X" warning

Ideally we'd detect this at build time and only warn if your build
was affected, but that's hard to do.  (Really we should just abort
when this scenario is detected rather than continuing, but now
users are relying on it.)

Hopefully improves issue #543.