clarify which parsing/syntax/unhandled errors are caught

My intuition is that if in evaluating try X else Y, several things can happend:

1. there is a parsing error anywhere in the line => error before any evaluation (e.g. try 1 else list 2)
2. there is a syntax error or interrupt in processing X => error during evaluation of X
3. there is any other type of error in processing X => no error and else Y is evaluated

(One inaccuracy here is what I call "parsing error" is printed as "syntax error" and what I call "syntax error" is printed mostly as "error: unhandled" but otherwise) it seems the case 2 above isn't accurate:

i13 : step
stdio:13:0:(3): error: unhandled step command

i14 : break
stdio:14:0:(3): error: unhandled break command

i15 : try (1+1; step) else 3

o15 = 3

i16 : try (1+1; break) else 3
stdio:16:10:(3): error: unhandled break command

We should probably review this code (there are also some nonexisting errors in the interpreter like "unhandled unwind command"?!)

Start by reproducing the listed try/else examples in the Macaulay2 interpreter and review the error-handling code that determines which failures are caught. Done means the behavior for parsing, syntax, interrupts, other errors, and the reported unhandled unwind command is clearly established and any inconsistencies are identified.