skip shebang in the first line

Something like this works now:

===
% PATH="./bin:$PATH" ./sum.ktscript 31 21
31 + 21 = 52

% cat sum.ktscript
#!/usr/bin/env kotlin -script

val a = Integer.parseInt(args[0])
val b = Integer.parseInt(args[1])
println("$a + $b = ${a + b}")
===

compiler/frontend/buildLexer.xml

@@ -24,7 +24,10 @@
               jvmargs="-Xmx512M"
               fork="true"
               failonerror="true">
+          <arg value="-charat"/>
+          <!-- generates invalid code when %line option is on
           <arg value="-sliceandcharat"/>
+          -->
           <arg value="-skel"/>
           <arg value="@{skeleton}"/>
           <arg value="-d"/>