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Fix Bug #602; APPLY with a primitive now copies the inputlist so that it can't be modified.

The fix was inspired by the source code for UCBLogo, which doesn't have this bug.
UCBLogo copies inputlist so that modifications won't affect any of the caller's variables.

However, instead of calling "append(argl, NIL)" this revision creates a new function
with a clearer name "copy_list(argl)".

Also, instead of always copying the list in APPLY, the list is only copied if the
procedure is the name of a primitive, since that's the only way (to my understanding)
the list could be modified. This was partly to only incur the overhead of copying
the list when a copy was needed, but also for clarity: the fix closer to the code
path that needs it.

Add unit tests for SUBSTRINGP

Fix an example in the documentation for MEMBER.

Add tests for MEMBER

Add more tests for MEMBERP based on a recent code review.

Improve a comment

Add more information to documentation for PAUSE, including how to exit pause mode.
This is part of Feature Request #136.

Fix a comment

Fix a comment

Remove trailing whitespace from the text of LOCALIZED_UNSAVEDCHANGES_MESSAGE1.
This looked like an accident, not something that was intended to be rendered in the dialog box.