Rescue and re-raise syntax errors in Template#parse to add line numbers.

This can be done now that the parse context has the line number
information, so it doesn't need to be added on closer to the original
exception.  This has the advantage of not having to rescue and re-raise the
exception multiple times, and simplifies liquid-c which would otherwise
have to rescue the exception in BlockBody#parse.

lib/liquid/parser_switching.rb

@@ -8,7 +8,6 @@ module Liquid
         begin
           return strict_parse_with_error_context(markup)
         rescue SyntaxError => e
-          e.line_number = line_number
           @options.warnings << e
           return lax_parse(markup)
         end
@@ -20,6 +19,7 @@ module Liquid
     def strict_parse_with_error_context(markup)
       strict_parse(markup)
     rescue SyntaxError => e
+      e.line_number = line_number
       e.markup_context = markup_context(markup)
       raise e
     end