Strange parse behavior (PR#8815)

Hi,

I discovered the following strange behavior in parse () on syntactically 
incorrect statements. This is on R 2.3.0 (linux). It may or may not have been 
present earlier than 2.3.0, but I only discovered it recently. I can see no 
mention of it in the NEWS file from trunk.

Consider these statements (the output I get is shown commented below each 
statement):

bad.syntax <- ")\nprint (\"hello\")\nprint (\"world\")"

try (parse (text=bad.syntax, n=-1))	# OK
# Error in parse(file, n, text, prompt) : syntax error in ")"
try (parse (text=bad.syntax, n=1))	# OK
# Error in parse(file, n, text, prompt) : syntax error in ")"
try (parse (text=bad.syntax, n=2))	# No error!
# NULL
try (parse (text=bad.syntax, n=3))	# No error!
# NULL
try (parse (text=bad.syntax, n=4))	# Misleading message
# Error in parse(file, n, text, prompt) : syntax error in:
# "print ("hello")
# print ("world")"

Probably there are not too many use cases of parse (n=x) with x not either -1 
or 1, so it should not be a grave problem, but it just doesn't look right.