proper Char comparison, despite weakly-typed Scala (cf. 5ff5208de089);

--- a/src/Pure/General/completion.scala	Mon Mar 10 22:39:37 2014 +0100
+++ b/src/Pure/General/completion.scala	Mon Mar 10 22:40:48 2014 +0100
@@ -217,7 +217,7 @@
     private def underscores: Parser[String] = "_*".r
 
     def is_word(s: CharSequence): Boolean = word_regex.pattern.matcher(s).matches
-    def is_word_char(c: Char): Boolean = Symbol.is_ascii_letdig(c) || c == "."
+    def is_word_char(c: Char): Boolean = Symbol.is_ascii_letdig(c) || c == '.'
 
     def extend_word(text: CharSequence, offset: Text.Offset): Text.Offset =
     {