fixing mwiede#131 issues (mwiede#134)

* log exceptions to logger instead of STDOUT/ERR, put class under test,
fixed bugs that where found in the process

 - fixed bug in remove(String, String, String) leading to only every
second host key being removed
 - ensure that there is a SHA1-hash-instance to prevent
NullPointerExceptions
 - replaced all occurrences of STDOUT/ERR outputs in case of exceptions
with log entries
 - added a default method to Logger to allow passing the exception to be
logged with the message

* create the exception we expect to get the exception message of that
particular JVM

* use platform dependent linebreak for logging the stack trace
added log-framework-specific implementations of log(int, String,
Throwable) to pass the cause to the framework in a fitting way
added tests for all log frameworks that can be configured in a
programmatic way.

* added

* "normalize" line breaks

* enforce \r\n when printing linebreaks

* fixed test to check the line break between message and stacktrace (that
actually is system dependent)

* make members final
use slf4j 1.x API for logging to keep backward compatibility

* throw a RuntimeException (to keep the signature of KnownHost's
constructor) if the HMAC-SHA1-class can't be instantiated.

src/main/java/com/jcraft/jsch/JulLogger.java

@@ -1,12 +1,20 @@
 package com.jcraft.jsch;
 
 import java.util.logging.Level;
+import java.util.logging.Logger;
 
 public class JulLogger implements com.jcraft.jsch.Logger {
 
-  private static final java.util.logging.Logger logger = java.util.logging.Logger.getLogger(JSch.class.getName());
+  private static final Logger stlogger = Logger.getLogger(JSch.class.getName());
+  private final Logger logger;
+
+  public JulLogger() {
+    this(stlogger);
+  }
 
-  public JulLogger() {}
+  JulLogger(Logger logger) {
+    this.logger = logger;
+  }
 
   @Override
   public boolean isEnabled(int level) {
@@ -15,10 +23,19 @@ public boolean isEnabled(int level) {
 
   @Override
   public void log(int level, String message) {
-    logger.log(getLevel(level), message);
+    log(level, message, null);
+  }
+
+  @Override
+  public void log(int level, String message, Throwable cause) {
+    if (cause == null) {
+      logger.log(getLevel(level), message);
+      return;
+    }
+    logger.log(getLevel(level), message, cause);
   }
 
-  private static Level getLevel(int level) {
+  static Level getLevel(int level) {
     switch (level) {
       case com.jcraft.jsch.Logger.DEBUG:
         return Level.FINE;