Make .bat start script honor -J and -D arguments.

This makes the .bat start script parse and use -J and -D arguments.

Specifically:
 - Parameters starting with `-J` are stripped of the prefix, unquoted if
   necessary and appended to `%JAVA_OPTS%`.
 - Parameters starting with `-D` are unquoted if necessary and then
   appended to the others. The right-hand side of a property can be
   quoted or not.
 - The exact arguments passed to the script are also given as-is to the
   main class (using `%*`), so, as before, the main class should ignore
   arguments starting with -J and -D. This could be improved by manually
   parsing all arguments (not just -J and -D), but this is a mine field
   when it comes to quoting and delimiters...

This is adapted from my similar contribution to scala 2.10, see
scala/scala#2767.

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I've wanted to do this for some time, so here it is. This is also somewhat related to #155.