Resolve "Disable logging messages in pure C++ code"

Closes #5 (closed)

I have implemented functionality to select the log level in pure C++ code. You can now simply use bob::core::log_level(bob::core::INFO) to allow INFO messages (and above) to be printed, or bob::core::log_level(bob::core::DISABLE) to disable all C++ log output. By default, DEBUG messages are written. This functionality should only be used in pure C++ code and is, therefore, not bound to python, which has its own logging system. The interface between bob and the logging system in Python has not changed.

I have created a new bob/core/_test.so extension, which contains test cases for the new functionality. To be able to run it using nose, the test case has been bound to Python. I have also moved the existing C++-only test cases, which have been in the bob/core/_library.so into the bob/core/_test.so. Hence, the test cases are not loaded any more when running import bob.core, but only during testing.

@andre.anjos : As you have written the logging system, I assign this PR to you.

bob/core/cpp/logging.cpp

@@ -140,12 +140,7 @@ bob::core::AutoOutputDevice::AutoOutputDevice()
 bob::core::AutoOutputDevice::AutoOutputDevice(const std::string& configuration)
 : m_device()
 {
-  std::string str(configuration);
-  str.erase(std::remove_if(str.begin(), str.end(), ::isspace), str.end());
-  if (str == "null" || str.size()==0) m_device.reset(new NullOutputDevice);
-  else if (str == "stdout") m_device.reset(new StdoutOutputDevice);
-  else if (str == "stderr") m_device.reset(new StderrOutputDevice);
-  else m_device.reset(new FileOutputDevice(configuration));
+  reset(configuration);
 }
 
 bob::core::AutoOutputDevice::AutoOutputDevice(boost::shared_ptr<OutputDevice> d)
@@ -156,6 +151,16 @@ bob::core::AutoOutputDevice::AutoOutputDevice(boost::shared_ptr<OutputDevice> d)
 bob::core::AutoOutputDevice::~AutoOutputDevice() {
 }
 
+void bob::core::AutoOutputDevice::reset(const std::string& configuration)
+{
+  std::string str(configuration);
+  str.erase(std::remove_if(str.begin(), str.end(), ::isspace), str.end());
+  if (str == "null" || str.size()==0) m_device.reset(new NullOutputDevice);
+  else if (str == "stdout") m_device.reset(new StdoutOutputDevice);
+  else if (str == "stderr") m_device.reset(new StderrOutputDevice);
+  else m_device.reset(new FileOutputDevice(configuration));
+}
+
 std::streamsize bob::core::AutoOutputDevice::write(const char* s, std::streamsize n) {
   return m_device->write(s, n);
 }
@@ -168,3 +173,10 @@ boost::iostreams::stream<bob::core::AutoOutputDevice> bob::core::debug("stdout")
 boost::iostreams::stream<bob::core::AutoOutputDevice> bob::core::info("stdout");
 boost::iostreams::stream<bob::core::AutoOutputDevice> bob::core::warn("stderr");
 boost::iostreams::stream<bob::core::AutoOutputDevice> bob::core::error("stderr");
+
+void bob::core::log_level(bob::core::LOG_LEVEL level){
+  bob::core::debug->reset(level == DEBUG ?  "stdout" : "null");
+  bob::core::info->reset(level >= INFO && level < DISABLE ?  "stdout" : "null");
+  bob::core::warn->reset(level >= WARNING && level < DISABLE ?  "stderr" : "null");
+  bob::core::error->reset(level >= ERROR && level < DISABLE ?  "stderr" : "null");
+}