Properly shut down LLVM on error

We were leaving the compiler running indefinitely whenever an exception
was encountered. This changes the code to properly close our output
stream when handling an exception.
Fix (make-parameter) to be GC safe

Neither The initial value or (currently unused) converter function were
being rooted across the allocation of the procedure cell. Because the
unit test only used a constant initial value this appeared to work
correctly.
Fix incorrect comment and message in symbol=?
Fix incorrect copy-and-pasted comments

The "64bit signed int" comment obviously only refers to boxing exact
integers