Fix spelling (#3967)

Author: garydgregory

log4j-1.2-api/src/main/java/org/apache/log4j/helpers/FileWatchdog.java

@@ -60,7 +60,7 @@ protected void checkAndConfigure() {
         try {
             fileExists = file.exists();
         } catch (final SecurityException e) {
-            LogLog.warn("Was not allowed to read check file existance, file:[" + filename + "].");
+            LogLog.warn("Was not allowed to read check file existence, file:[" + filename + "].");
             interrupted = true; // there is no point in continuing
             return;
         }

log4j-1.2-api/src/main/java/org/apache/log4j/helpers/PatternParser.java

@@ -188,7 +188,7 @@ public PatternConverter parse() {
                         formattingInfo.max = c - '0';
                         state = MAX_STATE;
                     } else {
-                        LogLog.error("Error occured in position " + i + ".\n Was expecting digit, instead got char \""
+                        LogLog.error("Error occurred in position " + i + ".\n Was expecting digit, instead got char \""
                                 + c + "\".");
                         state = LITERAL_STATE;
                     }
@@ -397,7 +397,7 @@ public String convert(final LoggingEvent event) {
             try {
                 converted = df.format(date);
             } catch (Exception ex) {
-                LogLog.error("Error occured while converting date.", ex);
+                LogLog.error("Error occurred while converting date.", ex);
             }
             return converted;
         }

log4j-core/src/main/java/org/apache/logging/log4j/core/util/datetime/FastDatePrinter.java

@@ -451,7 +451,7 @@ public String format(final long millis) {
 
     /**
      * Creates a String representation of the given Calendar by applying the rules of this printer to it.
-     * @param c the Calender to apply the rules to.
+     * @param c the Calendar to apply the rules to.
      * @return a String representation of the given Calendar.
      */
     private String applyRulesToString(final Calendar c) {