Document SQLTester's --print command and add some argument validation to it.

FossilOrigin-Name: ab9c945bb0b4210b3f47e6341f150f8a7cc45f9e4e4c2247e91d2528ed4772a6

ext/jni/src/org/sqlite/jni/tester/SQLTester.java

@@ -574,6 +574,9 @@ class OpenDbCommand extends Command {
 class PrintCommand extends Command {
   public PrintCommand(){}
   public void process(SQLTester t, String[] argv, String content) throws Exception{
+    if( 1==argv.length && null==content ){
+      Util.badArg(argv[0]," requires at least 1 argument or body content.");
+    }
     if( argv.length > 1 ) t.outln("\t",Util.argvToString(argv));
     if( null!=content ) t.outln(content.replaceAll("(?m)^", "\t"));
   }

ext/jni/src/org/sqlite/jni/tester/test-script-interpreter.md

@@ -244,3 +244,8 @@ respectively.  The difference is that column values are appended to the
 result buffer literally, without every enclosing the values in `{...}` or
 `"..."` and without escaping any characters in the column value and comparison
 is always an exact strcmp() not a GLOB.
+
+### The --print command
+
+The --print command emits both its arguments and its body (if any) to
+stdout, indenting each line of output.

ext/jni/src/tests/000_first.test

@@ -18,6 +18,7 @@ select 2;
 --oom
 --print These are args to the print command.
 This is from the print command's body.
+--print
 Also from the print command.
 --- also ignored
 --testcase first