ktest should give a warning when running K file and programs is specified but extensions missing

Resolves #138 and #209.

Running ktest using config.xml should work as before.

Difference is, when we run it using a .k file and specify "programs" attribute without specifying "extension", it prints a warning:

```
➜  lesson_1 git:(ktest-extension-eror) ✗ ktest lambda.k --skip "kompile pdf" --programs . --dry      
Running initial scripts...
SUCCESS
Running /home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/lambda.k programs... (0 in total, 0 with input, 0 with output, 0 with error)
SUCCESS
[Warning] Compiler: 'programs' attribute is given, but 'extension' is not.
ktest won't run any programs.
```

(note that this is not quite what I wanted -- I'd like to print the warning as first thing, instead of last thing. @dwightguth how can I do this?)

This works as before because default value of "programs" is used:

```
➜  lesson_1 git:(ktest-extension-eror) ✗ ktest lambda.k --skip "kompile pdf" --extension lambda --dry
Running initial scripts...
SUCCESS
Running /home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/lambda.k programs... (4 in total, 0 with input, 4 with output, 0 with error)
'/home/omer/K/k_new_dist/k/k-distribution/target/release/k/bin/krun' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/tests/free-variable-capture.lambda' '--directory' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1'
'/home/omer/K/k_new_dist/k/k-distribution/target/release/k/bin/krun' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/tests/closed-variable-capture.lambda' '--directory' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1'
'/home/omer/K/k_new_dist/k/k-distribution/target/release/k/bin/krun' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/tests/omega.lambda' '--directory' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1'
'/home/omer/K/k_new_dist/k/k-distribution/target/release/k/bin/krun' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1/tests/identity.lambda' '--directory' '/home/omer/K/k_new_dist/k/k-distribution/tutorial/1_k/1_lambda/lesson_1'
SUCCESS
```