avoid ConcurrentModificationExceptions on add-on update check
Fix: Once a groovy script has a compiletime error, it's never compiled again.

This includes changes:
- In execute(), re-raise existing errors only if the scrips has not
  changed.
- For this to work: reset ``compileTime`` prior to compiling the script.
  (Otherwise canUseOldCompiledScript() could not be run in execute() due
  to it integrated check-delay.)
- Clear ``errorsInScript`` prior to compiling. (Instead of not compiling,
  at all if ``errorsInScript are set.)
- Same changes for GenericScript.

Conflicts:
	freeplane_plugin_script/src/org/freeplane/plugin/script/GenericScript.java
Fix code-indent.

I did not put this into the last commit to reduce number of changes.

Conflicts:
	freeplane_plugin_script/src/org/freeplane/plugin/script/GenericScript.java
Move some methods to be side by side.
Rearrange some line to stop diffs in {Groovy,Generic}Script.execute easier.

Both should behave the same so spotting differences between the to
implementations should be made easy.
Fix: stdout not set in generic scripts.

Thus `print` was not working in e.g Python scripts.

Conflicts:
	freeplane_plugin_script/src/org/freeplane/plugin/script/GenericScript.java