SI-4907 SI-4615 scala.bat honors -J and -D options.

This makes scala.bat 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% or default values.
 - 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.
 - All of those are given to `java` before any other parameters.
 - The above only happens on parameter preceding the first parameter
   that does not start with "-" (usually a class name).
 - The exact arguments passed to scala.bat are also given as-is to
   the scala launcher (including -J and -D arguments).

   set JAVA_OPTS=-Xmx512m
   scala -J-Xmx128m -Dprop1=42 -Dprop2="hello world" "-Dprop3=bar"
"-J-Xms64m" Test foo

   will result in

   java -Xmx512m -Xmx128m -Dprop1=42 -Dprop2="hello world" -Dprop3=bar
-Xms64m [cp, scala main] -J-Xmx128m -Dprop1=42 -Dprop2="hello world"
"-Dprop3=bar" "-J-Xms64m" Test foo
Merge pull request #2767 from gourlaysama/t4907

SI-4907 SI-4615 scala.bat now honors -J and -D options.