Don't force shebang line in amalgamated script.

There may be Lua implementations that don't support shebang lines in
files or situations where you want to load amalgamated Lua code from
somewhere other than a file.

src/amalg.lua

@@ -395,17 +395,18 @@ local function amalgamate( ... )
     out = assert( io.open( oname, "w" ) )
   end
 
-  -- If a main script is to be embedded, this includes a shebang line
-  -- so that the resulting amalgamation can be run without explicitly
-  -- specifying the interpreter on unixoid systems.
+  -- If a main script is to be embedded, this includes the same
+  -- shebang line that was used in the main script, so that the
+  -- resulting amalgamation can be run without explicitly
+  -- specifying the interpreter on unixoid systems (if a shebang
+  -- line was specified in the first place, that is).
   local script_bytes, script_binary, shebang
   if script then
     script_bytes, script_binary, shebang = readluafile( script )
     if shebang then
-      out:write( shebang, "\n\ndo\n\n" )
-    else
-      out:write( "#!/usr/bin/env lua\n\ndo\n\n" )
+      out:write( shebang, "\n\n" )
     end
+    out:write( "do\n\n" )
   end
 
   -- Sort modules alphabetically. Modules will be embedded in