Trying to parse this invalid LPF syntax:
LOCATE COMP "a" SITE "A1"
IOBUF PORT "a" IO_TYPE=LVCMOS33;
(note missing semicolon on first line) gives an assertion failure in
strip_quotes, because the fifth token is scanned as "A1"IOBUF (without
a trailing quote).
Avoid the problem by detecting extraneous input and issuing a more
specific error.
