math/abacus: unbreak build on 10.1R (clang 3.4.1)

sources/ostream.cc:290:16: error: declaration conflicts with target of using

    declaration already in scope
ABA_OSTREAM& endl(ABA_OSTREAM &o)
             ^

./Include/abacus/ostream.h:48:14: note: target of using declaration
ABA_OSTREAM& endl(ABA_OSTREAM &o);

^

./Include/abacus/ostream.h:50:9: note: using declaration
using ::endl;

^

sources/ostream.cc:293:11: error: 'on_' is a private member of 'ABA_OSTREAM'

if (o.on_) o.out_ << flush;
      ^

./Include/abacus/ostream.h:225:17: note: declared private here

bool      on_;
          ^

sources/ostream.cc:293:18: error: 'out_' is a private member of 'ABA_OSTREAM'

if (o.on_) o.out_ << flush;
             ^

./Include/abacus/ostream.h:220:17: note: declared private here

ostream  &out_;
          ^

sources/ostream.cc:294:10: error: 'logOn_' is a private member of 'ABA_OSTREAM'

if(o.logOn_) *(o.log_) << flush;
     ^

./Include/abacus/ostream.h:230:17: note: declared private here

bool      logOn_;
          ^

sources/ostream.cc:294:22: error: 'log_' is a private member of 'ABA_OSTREAM'

if(o.logOn_) *(o.log_) << flush;
                 ^

./Include/abacus/ostream.h:234:17: note: declared private here

ofstream *log_;
          ^

Tested by: md5 ostream.o (gcc5, clang36)