rewrite string parsing to avoid unlimited lookahead * NEWS: Mention change. * lex.h, lex.ll (lexical_feedback::string_text, lexical_feedback::string_line, lexical_feedback::string_column): New data members (lexical_feedback::lexical_feedback): Initialize them. (lexical_feedback::reset): Initialize them. (octave_base_lexer::begin_string): New function. (\", "'", <COMMAND_START>[\"\']): Use begin_string to set start state * instead of calling handle_string to parse string. (DQ_STRING_START, SQ_STRING_START): New exclusive start states. (<DQ_STRING_START>\"\", <DQ_STRING_START>\", <DQ_STRING_START>{NL}, <DQ_STRING_START>\\[0-7]{1,3}, <DQ_STRING_START>"\\a", <DQ_STRING_START>"\\b", <DQ_STRING_START>"\\f", <DQ_STRING_START>"\\n", <DQ_STRING_START>"\\r", <DQ_STRING_START>"\\t", <DQ_STRING_START>"\\v", <DQ_STRING_START>\\{ANY_INCLUDING_NL}, <DQ_STRING_START>[^\\\n\"]+, <SQ_STRING_START>[^\'\n\r]*\', <SQ_STRING_START>{NL}): New rules for parsing character strings. (octave_base_lexer::have_continuation, octave_base_lexer::have_ellipsis_continuation, octave_base_lexer::handle_string): Delete.

--- a/NEWS
+++ b/NEWS
@@ -77,6 +77,17 @@
      c,...
     ] = deal (1,2,3)
 
+ ** Line continuations inside character strings have changed.
+
+    The sequence '...' is no longer recognized as a line continuations
+    are inside character strings.  A backslash followed by a newline
+    character is no longer recognized as a line continuation inside
+    single-quoted character strings.  Inside double-quoted character
+    strings, a backslash followed by a newline character is still
+    recognized as a line continuation but the backslash character must
+    be followed immediately by the newline character.  No whitespace or
+    end-of-linecomment may appear between them.
+
  ** Warning IDs renamed:
 
     Octave:array-as-scalar => Octave:array-to-scalar