Add -Xverify:none to tests and docs

On newer versions of java bytecode is verified before it is run.  Since
this agent modifies core java bytecode it needs to bypass this
verification.  To turn the verification off pass -Xverify:none as an
argument when running the agent.  Fixed in unit tests and docs.

Details: https://www.ibm.com/support/pages/ibm-java-linux-howto-resolving-javalangverifyerror-jvmvrfy012-stack-shape-inconsistent

pom.xml

@@ -55,7 +55,7 @@
               <exclude>**/TransformerTest.java</exclude>
             </excludes>
             <argLine>
-              -javaagent:"${project.build.directory}/file-leak-detector-${project.version}-jar-with-dependencies.jar"
+              -javaagent:"${project.build.directory}/file-leak-detector-${project.version}-jar-with-dependencies.jar" -Xverify:none
             </argLine>
           </configuration>
         </execution>

src/site/apt/index.apt

@@ -14,28 +14,34 @@ What is this?
     dependency jar and the list of the table can be
     {{{http://file-leak-detector.kohsuke.org/apidocs/index.html?org/kohsuke/file_leak_detector/Listener.html}programmatically accessed}}.
 
+Warning
+
+    The agent modifies the bytecode of core java classes, which causes java bytecode
+    validation to fail ({{{https://www.ibm.com/support/pages/ibm-java-linux-howto-resolving-javalangverifyerror-jvmvrfy012-stack-shape-inconsistent}details}}).  For it to work in newer version
+    of java you need the include the -Xverify:none flag when running the javaagent.
+
 Usage
 
     Without any option, this tool silently records file open/close operations
     and upon "too many open files" exception, the table will be dumped to
     stderr.
 
 -------------
-$ java -javaagent:path/to/file-leak-detector.jar ...your usual Java args follows...
+$ java -javaagent:path/to/file-leak-detector.jar -Xverify:none ...your usual Java args follows...
 -------------
 
     There are several options you can pass to the agent. For example, to
     dump the open file handles when the total number reaches 200, you can do the following:
 
 -------------
-$ java -javaagent:path/to/file-leak-detector.jar=threshold=200 ...your usual Java args follows...
+$ java -javaagent:path/to/file-leak-detector.jar=threshold=200 -Xverify:none ...your usual Java args follows...
 -------------
 
     Or have it run a mini HTTP server so that you can access the information
     from your browser, do the followind and open http://localhost:19999/:
 
 -------------
-$ java -javaagent:path/to/file-leak-detector.jar=http=19999 ...your usual Java args follows...
+$ java -javaagent:path/to/file-leak-detector.jar=http=19999 -Xverify:none ...your usual Java args follows...
 -------------
 
     Use the help option to see the help screen for the complete list of options.
@@ -52,5 +58,5 @@ Attaching after VM startup
     in the same format you do to the agent.
 
 -------------
-$ java -jar path/to/file-leak-detector.jar 1500 threshold=200,strong
+$ java -jar path/to/file-leak-detector.jar 1500 threshold=200,strong -Xverify:none
 -------------