Allow CaptureLog's consumer to specify desired log level.

Of course, given the way the log machinery works, it's really "everything at
that level or stronger."

indra/llcommon/tests/wrapllerrs.h

@@ -87,7 +87,7 @@ struct WrapLL_ERRS
 class CaptureLog : public LLError::Recorder
 {
 public:
-    CaptureLog():
+    CaptureLog(LLError::ELevel level=LLError::LEVEL_DEBUG):
         // Mostly what we're trying to accomplish by saving and resetting
         // LLError::Settings is to bypass the default RecordToStderr and
         // RecordToWinDebug Recorders. As these are visible only inside
@@ -100,7 +100,7 @@ class CaptureLog : public LLError::Recorder
         mOldSettings(LLError::saveAndResetSettings())
     {
         LLError::setFatalFunction(wouldHaveCrashed);
-        LLError::setDefaultLevel(LLError::LEVEL_DEBUG);
+        LLError::setDefaultLevel(level);
         LLError::addRecorder(this);
     }