GCC 6 build

* GCC 6 defaults to -std=gnu++14, and attempting to build fldigi fails
    with a number of errors. One is that C++11 added std::next and so
    because of the "using namespace std" in src/fsq/fsq.cxx the global
    variable 'next' and std::next are ambiguous. That can be easily solved
    by qualifying ::next or adding using ::next at function scope.

  * The other errors are due to the different return type for
    std::complex<T>::real() and std::complex<T>::imag() in C++11 and
    later.

src/fsq/fsq.cxx

@@ -1195,9 +1195,10 @@ int fsq::rx_process(const double *buf, int len)
 						&rx_stream[SHIFT_SIZE],				// from
 						BLOCK_SIZE*sizeof(*rx_stream));	// # bytes
 				memset(fft_data, 0, sizeof(fft_data));
-				for (int i = 0; i < BLOCK_SIZE; i++)
-					fft_data[i].real() = fft_data[i].imag() =
-						rx_stream[i] * a_blackman[i];
+				for (int i = 0; i < BLOCK_SIZE; i++) {
+					double d = rx_stream[i] * a_blackman[i];
+					fft_data[i] = cmplx(d, d);
+				}
 				fft->ComplexFFT(fft_data);
 				process_tones();
 			}
@@ -1449,6 +1450,7 @@ double fsq_xmtdelay() // in seconds
 
 void fsq_repeat_last_command()
 {
+	using ::next;  // disambiguate from std::next
 	fsq_tx_text->clear();
 	fsq_tx_text->addstr(sz2utf8(commands[next].c_str()));
 	next++;
@@ -1494,7 +1496,7 @@ void try_transmit(void *)
 	if (active_modem != fsq_modem) return;
 
 	if (!active_modem->fsq_squelch_open() && trx_state == STATE_RX) {
-		next = 0;
+		::next = 0;
 		fsq_que_clear();
 //LOG_WARN("%s", "start_tx()");
 		start_tx();

src/ifkp/ifkp.cxx

@@ -580,9 +580,10 @@ int ifkp::rx_process(const double *buf, int len)
 						&rx_stream[IFKP_SHIFT_SIZE],			// from
 						IFKP_BLOCK_SIZE*sizeof(*rx_stream));	// # bytes
 				memset(fft_data, 0, sizeof(fft_data));
-				for (int i = 0; i < IFKP_BLOCK_SIZE; i++)
-					fft_data[i].real() = fft_data[i].imag() =
-						rx_stream[i] * a_blackman[i];
+				for (int i = 0; i < IFKP_BLOCK_SIZE; i++) {
+					double d = rx_stream[i] * a_blackman[i];
+					fft_data[i] = cmplx(d,d);
+				}
 				fft->ComplexFFT(fft_data);
 				process_tones();
 			}