allow backslash at end of line (during parsing)

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ParserGeneration.java

@@ -73,6 +73,7 @@ public class ParserGeneration {
         "allow multiple semicolons in {}",
         "allow .. as identifier",
         "rename Operator class",
-        "remove FieldAccess, small refactorings"
+        "remove FieldAccess, small refactorings",
+        "allow backslash at line end"
     };
 }

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/R.g

@@ -746,6 +746,7 @@ fragment ESCAPE [StringBuilder buf]
       | '\'' { buf.append('\''); }
       | ' ' { buf.append(' '); }
       | '\\' { buf.append('\\'); }
+      | '\n' { buf.append('\n'); }
       | a = OCT_DIGIT b = OCT_DIGIT c = OCT_DIGIT { buf.append(ParseUtil.octChar($a.text, $b.text, $c.text)); }
       | a = OCT_DIGIT b = OCT_DIGIT { buf.append(ParseUtil.octChar($a.text, $b.text)); }
       | a = OCT_DIGIT { buf.append(ParseUtil.octChar($a.text)); }